Robotics Club

C N Kapsalas, J S Sakellariou, P N Koustoumpardis and N A Aspragathos. An ARX-based method for the vibration control of flexible beams manipulated by industrial robots. Robotics and Computer-Integrated Manufacturing, 2017. URL, AbstractAbstract The vibration control problem of flexible objects manipulated by industrial robots under normal production conditions is investigated. This is an important problem as the quick and precise manipulation of such objects may reduce the production lead time and thus its cost. The problem is in the present study tackled for flexible beams via a novel method which overcomes various practical difficulties and can be easily applied in industrial environments with the least human intervention. The method is based on: (i) AutoRegressive with eXogenous (ARX) input stochastic modeling of the robot-beam system using exclusively experimental data, (ii) the design of an appropriate control system consisting of a typical feedforward PID-type controller and a feedback that enables the attenuation of the force at the robot's wrist and thus the suppression of the vibration at the beam's free-end and, (iii) a synthetic environment within which the performance of the control system may be tested under realistic operating conditions through simulation before its final implementation in the robot. The effectiveness of the method is experimentally assessed through the vibration control of a flexible metallic beam that is manipulated by an industrial robot for its insertion into a slot, testing additionally the control system's performance under various operating conditions for which it is not designed to deal with.BibTeX

@article{KAPSALAS2017,
title = "An ARX-based method for the vibration control of flexible beams manipulated by industrial robots",
journal = "Robotics and Computer-Integrated Manufacturing",
year = 2017,
issn = "0736-5845",
doi = "https://doi.org/10.1016/j.rcim.2017.11.001",
url = "http://www.sciencedirect.com/science/article/pii/S0736584517300054",
author = "C.N. Kapsalas and J.S. Sakellariou and P.N. Koustoumpardis and N.A. Aspragathos",
keywords = "Industrial robot, Vibration control, Flexible beam, ARX modeling, PID controller, System identification",
abstract = "Abstract The vibration control problem of flexible objects manipulated by industrial robots under normal production conditions is investigated. This is an important problem as the quick and precise manipulation of such objects may reduce the production lead time and thus its cost. The problem is in the present study tackled for flexible beams via a novel method which overcomes various practical difficulties and can be easily applied in industrial environments with the least human intervention. The method is based on: (i) AutoRegressive with eXogenous (ARX) input stochastic modeling of the robot-beam system using exclusively experimental data, (ii) the design of an appropriate control system consisting of a typical feedforward PID-type controller and a feedback that enables the attenuation of the force at the robot's wrist and thus the suppression of the vibration at the beam's free-end and, (iii) a synthetic environment within which the performance of the control system may be tested under realistic operating conditions through simulation before its final implementation in the robot. The effectiveness of the method is experimentally assessed through the vibration control of a flexible metallic beam that is manipulated by an industrial robot for its insertion into a slot, testing additionally the control system's performance under various operating conditions for which it is not designed to deal with."
}

V Syrimpeis, V Moulianitis, N A Aspragathos and E Panagiotopoulos. A knowledge based system for the selection of muscles for gait phase detection using EMGs. International Journal of Healthcare Information Systems and Informatics 12(2):18-45, 2017. URLBibTeX

P Sotiropoulos and N Aspragathos. Neural Networks to determine task oriented dexterity indices for an Underwater Vehicle-Manipulator System. Applied Soft Computing ():-, 2016. URL, AbstractAbstract A method for the fast approximation of dexterity indices for given underwater vehicle-manipulator systems (UVMS) configurations is presented. Common underwater tasks are associated with two well-known dexterity indices and two types of neural networks are designed and trained to approximate each one of them. The method avoids the lengthy calculation of the Jacobian, its determinant and the computationally expensive procedure of singular value decomposition required to compute the dexterity indices. It provides directly and in a considerably reduced computational time the selected dexterity index value for the given configuration of the system. The full kinematic model of the UVMS is considered and the NN training dataset is formulated by the conventional calculation of the selected dexterity indices. A comparison between the computational cost of the analytical calculation of the indices and their approximation by the two NN is presented for the validation of the proposed approach. This paper contributes mainly on broadening the applications of NN to a problem of high complexity and of high importance for UVMS high performance intervention.BibTeX

@article{Sotiropoulos2016,
title = "Neural Networks to determine task oriented dexterity indices for an Underwater Vehicle-Manipulator System",
journal = "Applied Soft Computing",
volume = "",
number = "",
pages = "-",
year = 2016,
note = "",
issn = "1568-4946",
doi = "http://dx.doi.org/10.1016/j.asoc.2016.08.033",
url = "http://www.sciencedirect.com/science/article/pii/S1568494616304276",
author = "P. Sotiropoulos and N. Aspragathos",
keywords = "High performance of underwater vehicle-manipulator systems",
abstract = "Abstract A method for the fast approximation of dexterity indices for given underwater vehicle-manipulator systems (UVMS) configurations is presented. Common underwater tasks are associated with two well-known dexterity indices and two types of neural networks are designed and trained to approximate each one of them. The method avoids the lengthy calculation of the Jacobian, its determinant and the computationally expensive procedure of singular value decomposition required to compute the dexterity indices. It provides directly and in a considerably reduced computational time the selected dexterity index value for the given configuration of the system. The full kinematic model of the \{UVMS\} is considered and the \{NN\} training dataset is formulated by the conventional calculation of the selected dexterity indices. A comparison between the computational cost of the analytical calculation of the indices and their approximation by the two \{NN\} is presented for the validation of the proposed approach. This paper contributes mainly on broadening the applications of \{NN\} to a problem of high complexity and of high importance for \{UVMS\} high performance intervention."
}

Fotios Dimeas and Nikos Aspragathos. Online stability in human-robot cooperation with admittance control. Haptics, IEEE Transactions on 9(2):267–278, 2016. URL, AbstractIn the design of a compliant admittance controller for physical human-robot interaction it is necessary to ensure stable and effective cooperation. The stability of the admittance controller is mainly threatened by a stiff environment. Many methods that guarantee stability in arbitrary environments, impose conservative control gains that limit the effectiveness of the cooperation. Inspired by previous work in frequency domain stability observers, a method is proposed in this paper to detect unstable behavior and stabilize the robot with online adaptation of the admittance control gains. The introduced instability index is based on frequency domain analysis, which very quickly detects unstable behavior by monitoring high frequency oscillation in the force signal. To treat the instability, an adaptation scheme of the admittance parameters is proposed, that relaxes conservative gains and improves the cooperation by considering the effect of variable admittance on the operators’ effort. We investigate two human-robot co-manipulation tasks; cooperation within a zero stiffness environment and cooperation in contact with a stiff double-wall virtual environment. The proposed methods are validated experimentally with a number of subjects in cooperation with an LWR manipulator.BibTeX

@article{Dimeas2016,
author = "Dimeas, Fotios and Aspragathos, Nikos",
journal = "Haptics, IEEE Transactions on",
title = "Online stability in human-robot cooperation with admittance control",
year = 2016,
volume = 9,
number = 2,
pages = "267--278",
abstract = "In the design of a compliant admittance controller for physical human-robot interaction it is necessary to ensure stable and effective cooperation. The stability of the admittance controller is mainly threatened by a stiff environment. Many methods that guarantee stability in arbitrary environments, impose conservative control gains that limit the effectiveness of the cooperation. Inspired by previous work in frequency domain stability observers, a method is proposed in this paper to detect unstable behavior and stabilize the robot with online adaptation of the admittance control gains. The introduced instability index is based on frequency domain analysis, which very quickly detects unstable behavior by monitoring high frequency oscillation in the force signal. To treat the instability, an adaptation scheme of the admittance parameters is proposed, that relaxes conservative gains and improves the cooperation by considering the effect of variable admittance on the operators’ effort. We investigate two human-robot co-manipulation tasks; cooperation within a zero stiffness environment and cooperation in contact with a stiff double-wall virtual environment. The proposed methods are validated experimentally with a number of subjects in cooperation with an LWR manipulator.",
keywords = "Admittance;Force;Frequency-domain analysis;Oscillators;Robots;Stability criteria;Compliance and Impedance Control;Low Effort Cooperation;Physical Human-Robot Interaction;Stability",
doi = "10.1109/TOH.2016.2518670",
url = "http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=7384497",
issn = "1939-1412",
month = ""
}

Panagiotis Sotiropoulos, Vasileios Kolonias, Nikos Aspragathos and Efthymios Housos. Rapid motion planning algorithm for optimal UVMS interventions in semi-structured environments using GPUs. Robotics and Autonomous Systems ():-, 2015. URL, AbstractAbstract In this work, a novel local motion planning algorithm is presented, for underwater vehicle manipulator systems (UVMS) that perform autonomous underwater inspection operations. An optimization problem is formulated considering the collision avoidance, the approximation of the given task curve and critical optimization criteria. The searching method is based on an evolutionary algorithm and it is able to generate a local motion plan using continuously updated sensor information. The working environment is represented by a Bump-surface entity, constantly updated by a parallel algorithm implemented on a graphical processing unit (GPU). A trained artificial neural network is used for the fast approximation of the considered dexterity index. The local planner can cope with unknown obstacles inside the workspace while executing the task and pursuing high performance configurations in the free space. A welding inspection on an underwater tube structure is considered as the validation scenario, while a UVMS with a mounted six degrees of freedom manipulator is assigned to perform the task.BibTeX

@article{Sotiropoulos2015,
title = "Rapid motion planning algorithm for optimal UVMS interventions in semi-structured environments using GPUs",
journal = "Robotics and Autonomous Systems",
volume = "",
number = "",
pages = "-",
year = 2015,
note = "",
issn = "0921-8890",
doi = "http://dx.doi.org/10.1016/j.robot.2015.06.005",
url = "http://www.sciencedirect.com/science/article/pii/S0921889015001335",
author = "Panagiotis Sotiropoulos and Vasileios Kolonias and Nikos Aspragathos and Efthymios Housos",
abstract = "Abstract In this work, a novel local motion planning algorithm is presented, for underwater vehicle manipulator systems (UVMS) that perform autonomous underwater inspection operations. An optimization problem is formulated considering the collision avoidance, the approximation of the given task curve and critical optimization criteria. The searching method is based on an evolutionary algorithm and it is able to generate a local motion plan using continuously updated sensor information. The working environment is represented by a Bump-surface entity, constantly updated by a parallel algorithm implemented on a graphical processing unit (GPU). A trained artificial neural network is used for the fast approximation of the considered dexterity index. The local planner can cope with unknown obstacles inside the workspace while executing the task and pursuing high performance configurations in the free space. A welding inspection on an underwater tube structure is considered as the validation scenario, while a \{UVMS\} with a mounted six degrees of freedom manipulator is assigned to perform the task."
}

A I Synodinos, V C Moulianitis and N A Aspragathos. A fuzzy approximation to dexterity measures of mobile manipulators. Advanced Robotics 0(0):1-17, 2015. URL, AbstractIn this paper, a fuzzy system is trained to approximate the manipulability index and the inverted condition number of a mobile manipulator. The kinematic model of a mobile platform with the attached manipulator is fused using twist theory and certain dexterity measures are examined throughout the configuration space. A Takagi–Sugeno–Kang fuzzy system is designed to approximate the dexterity measures and it is evaluated both for its error and its efficiency in computational cost. The proposed methodology is proved as a very efficient approximation that can be utilized in real-time motion planning algorithms without significantly adding computational cost to the controller.BibTeX

@article{Synodinos2015a,
author = "Synodinos, A.I. and Moulianitis, V.C. and Aspragathos, N.A.",
title = "A fuzzy approximation to dexterity measures of mobile manipulators",
journal = "Advanced Robotics",
volume = 0,
number = 0,
pages = "1-17",
year = 2015,
doi = "10.1080/01691864.2015.1015444",
url = "http://dx.doi.org/10.1080/01691864.2015.1015444",
eprint = "http://dx.doi.org/10.1080/01691864.2015.1015444",
abstract = "In this paper, a fuzzy system is trained to approximate the manipulability index and the inverted condition number of a mobile manipulator. The kinematic model of a mobile platform with the attached manipulator is fused using twist theory and certain dexterity measures are examined throughout the configuration space. A Takagi–Sugeno–Kang fuzzy system is designed to approximate the dexterity measures and it is evaluated both for its error and its efficiency in computational cost. The proposed methodology is proved as a very efficient approximation that can be utilized in real-time motion planning algorithms without significantly adding computational cost to the controller."
}

C Valsamos, V C Moulianitis, A I Synodinos and N A Aspragathos. Introduction of the high performance area measure for the evaluation of metamorphic manipulator anatomies. Mechanism and Machine Theory 86(0):88 - 107, 2015. URL, AbstractAbstract The modular metamorphic manipulator has been proposed in previous work as a concept of a robotic manipulator, where a single structure could be metamorphosed offline to different anatomies. In this paper, a global kinematic measure for the evaluation of the emerging anatomies, of a given structure of a class of 3 d.o.f. modular metamorphic manipulators is introduced. The proposed high performance area (HPA) measure depicts the dexterous workspace defined by a chosen threshold of a local kinematic index to meet the specifications of the given task. The region of the anatomy's workspace, where the selected local kinematic index meets the specifications is cross-sectioned by the XZ-plane in C-space, and the maximum area formed is the HPA. In order to reduce the computational burden, a procedure is proposed to approximate the HPA. The HPA is used to formulate an optimization problem for the determination of the optimal anatomy of a given metamorphic structure, which is solved using a genetic algorithm. A case study application of a 3 d.o.f. metamorphic structure is presented, using the manipulability measure and the conditioning index as local indices. The presented results are thoroughly discussed and the paper concludes with some hints for future work.BibTeX

@article{Valsamos201588,
title = "Introduction of the high performance area measure for the evaluation of metamorphic manipulator anatomies",
journal = "Mechanism and Machine Theory",
volume = 86,
number = 0,
pages = "88 - 107",
year = 2015,
note = "",
issn = "0094-114X",
doi = "http://dx.doi.org/10.1016/j.mechmachtheory.2014.11.012",
url = "http://www.sciencedirect.com/science/article/pii/S0094114X14002894",
author = "C. Valsamos and V.C. Moulianitis and A.I. Synodinos and N.A. Aspragathos",
keywords = "Modular robots",
abstract = "Abstract The modular metamorphic manipulator has been proposed in previous work as a concept of a robotic manipulator, where a single structure could be metamorphosed offline to different anatomies. In this paper, a global kinematic measure for the evaluation of the emerging anatomies, of a given structure of a class of 3 d.o.f. modular metamorphic manipulators is introduced. The proposed high performance area (HPA) measure depicts the dexterous workspace defined by a chosen threshold of a local kinematic index to meet the specifications of the given task. The region of the anatomy's workspace, where the selected local kinematic index meets the specifications is cross-sectioned by the XZ-plane in C-space, and the maximum area formed is the HPA. In order to reduce the computational burden, a procedure is proposed to approximate the HPA. The \{HPA\} is used to formulate an optimization problem for the determination of the optimal anatomy of a given metamorphic structure, which is solved using a genetic algorithm. A case study application of a 3 d.o.f. metamorphic structure is presented, using the manipulability measure and the conditioning index as local indices. The presented results are thoroughly discussed and the paper concludes with some hints for future work."
}

Fotios Dimeas, L D Avendaño-Valencia and Nikos Aspragathos. Human - robot collision detection and identification based on fuzzy and time series modelling. Robotica FirstView:1–13, May 2014. URL, AbstractABSTRACT SUMMARY In this paper, two methods are proposed and implemented for collision detection between the robot and a human based on fuzzy identification and time series modelling. Both methods include a collision detection system for each joint of the robot that is trained to approximate the external torque. In addition, the proposed methods are able to detect the occurrence of a collision, the link that collided and to some extent the magnitude of the collision without using the explicit model of the robot. Since the speed of the detection is of critical importance for mitigating the danger, attention is paid to recognise a collision as soon as possible. Experimental results conducted with a KUKALWR manipulator using two joints in planar motion, verify the validity on both methods.BibTeX

@article{Dimeas2014b,
author = "Dimeas,Fotios and Avendaño-Valencia,L. D. and Aspragathos,Nikos",
title = "Human - robot collision detection and identification based on fuzzy and time series modelling",
journal = "Robotica",
volume = "FirstView",
month = 5,
year = 2014,
issn = "1469-8668",
pages = "1--13",
numpages = 13,
doi = "10.1017/S0263574714001143",
url = "http://journals.cambridge.org/article_S0263574714001143",
abstract = "ABSTRACT SUMMARY In this paper, two methods are proposed and implemented for collision detection between the robot and a human based on fuzzy identification and time series modelling. Both methods include a collision detection system for each joint of the robot that is trained to approximate the external torque. In addition, the proposed methods are able to detect the occurrence of a collision, the link that collided and to some extent the magnitude of the collision without using the explicit model of the robot. Since the speed of the detection is of critical importance for mitigating the danger, attention is paid to recognise a collision as soon as possible. Experimental results conducted with a KUKALWR manipulator using two joints in planar motion, verify the validity on both methods."
}

Fotios Dimeas, Dhionis V Sako, Vassilis C Moulianitis and Nikos A Aspragathos. Design and fuzzy control of a robotic gripper for efficient strawberry harvesting. Robotica FirstView:1–14, May 2014. URL, AbstractABSTRACT SUMMARY Strawberry is a very delicate fruit that requires special treatment during harvesting. A hierarchical control scheme is proposed based on a fuzzy controller for the force regulation of the gripper and proper grasping criteria, that can detect misplaced strawberries on the gripper or uneven distribution of forces. The design of the gripper and the controller are based on conducted experiments to measure the maximum gripping force and the required detachment force under a variety of detachment techniques. It is demonstrated that the hand motion for detaching the fruit from the stem has a significant role in the process because it can reduce the required force. By analysing those results a robotic gripper with pressure profile sensors is developed that demonstrates an efficiency comparable to the human hand for strawberry grasping. The designed gripper and fuzzy controller performance is tested with a considerable number of fresh fruits to demonstrate the effectiveness to the uncertainties of strawberry grasping.BibTeX

@article{Dimeas2014a,
author = "Dimeas,Fotios and Sako,Dhionis V. and Moulianitis,Vassilis C. and Aspragathos,Nikos A.",
title = "Design and fuzzy control of a robotic gripper for efficient strawberry harvesting",
journal = "Robotica",
volume = "FirstView",
month = 5,
year = 2014,
issn = "1469-8668",
pages = "1--14",
numpages = 14,
doi = "10.1017/S0263574714001155",
url = "http://journals.cambridge.org/article_S0263574714001155",
abstract = "ABSTRACT SUMMARY Strawberry is a very delicate fruit that requires special treatment during harvesting. A hierarchical control scheme is proposed based on a fuzzy controller for the force regulation of the gripper and proper grasping criteria, that can detect misplaced strawberries on the gripper or uneven distribution of forces. The design of the gripper and the controller are based on conducted experiments to measure the maximum gripping force and the required detachment force under a variety of detachment techniques. It is demonstrated that the hand motion for detaching the fruit from the stem has a significant role in the process because it can reduce the required force. By analysing those results a robotic gripper with pressure profile sensors is developed that demonstrates an efficiency comparable to the human hand for strawberry grasping. The designed gripper and fuzzy controller performance is tested with a considerable number of fresh fruits to demonstrate the effectiveness to the uncertainties of strawberry grasping."
}

C Valsamos, V Moulianitis and N Aspragathos. Kinematic Synthesis and Evaluation of Structure Topologies for Metamorphic Serial Manipulators. ASME Journal of Mechanisms and Robotics 6(4):14, 2014. URL, AbstractIn this work a method for the kinematic synthesis of structure topologies for modular metamorphic serial manipulators is presented. A detailed description of this class of robot manipulators is presented, in order to clarify their basic elements and their basic structural definitions. Based on these, the metamorphic structure representation (MSR) is proposed for the systematic representation of this type of metamorphic manipulator structures. A thorough examination of the possible metamorphic links that can be constructed is presented and used for the definition of the manipulator's structure evaluation criteria, to formulate a multicriteria evaluation index. The problem of the optimal kinematic synthesis of metamorphic structures is formulated and the process of automated generation of structures according to the specified requirements is presented. The results are presented in detail, in order to reflect their validity and the advantages that the proposed process for the kinematic synthesis of topologies for the modular metamorphic manipulator provides to the designer.BibTeX

@article{Valsamos2014,
title = "Kinematic Synthesis and Evaluation of Structure Topologies for Metamorphic Serial Manipulators",
journal = "ASME Journal of Mechanisms and Robotics",
author = "C. Valsamos and V. Moulianitis and N. Aspragathos",
year = 2014,
volume = 6,
number = 4,
pages = 14,
url = "http://mechanismsrobotics.asmedigitalcollection.asme.org/article.aspx?articleid=1876665",
doi = "10.1115/1.4027741",
abstract = "In this work a method for the kinematic synthesis of structure topologies for modular metamorphic serial manipulators is presented. A detailed description of this class of robot manipulators is presented, in order to clarify their basic elements and their basic structural definitions. Based on these, the metamorphic structure representation (MSR) is proposed for the systematic representation of this type of metamorphic manipulator structures. A thorough examination of the possible metamorphic links that can be constructed is presented and used for the definition of the manipulator's structure evaluation criteria, to formulate a multicriteria evaluation index. The problem of the optimal kinematic synthesis of metamorphic structures is formulated and the process of automated generation of structures according to the specified requirements is presented. The results are presented in detail, in order to reflect their validity and the advantages that the proposed process for the kinematic synthesis of topologies for the modular metamorphic manipulator provides to the designer."
}

Stavros G Papageorgiou and Nikos A Aspragathos. Five-axis flank milling of dually defined twisted ruled surfaces. Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture 228(3):356-366, 2014. URL, AbstractThis article presents an approach based on screw theory and line geometry for the flank milling of dually defined twisted ruled surfaces. The designed surface is defined by a single-parametric dual nonuniform rational basis spline representation, while the tool’s axis is represented by a dual unit vector. The machining is performed along the dually defined lines and not per point since the ruled surface is represented by an aggregate of lines. The initial locating of the tool is accomplished via dual vector algebra and line geometry. Our method results in compact algorithms and fast tool-position calculation due to the single-parametric definition of the ruled surface and to the dual orthogonal matrix operator that is utilized to spatially associate the tool and the surface. The tool path determination is based on the offset of the designed surface. An iterative algorithm is introduced to ensure interference-free tool path that eliminates overcut. The introduced approach can be applied to twisted ruled surfaces and is appropriate for the machining of blades, propellers and turbines.BibTeX

@article{Papageorgiou01032014,
author = "Papageorgiou, Stavros G and Aspragathos, Nikos A",
title = "Five-axis flank milling of dually defined twisted ruled surfaces",
volume = 228,
number = 3,
pages = "356-366",
year = 2014,
doi = "10.1177/0954405413501501",
abstract = "This article presents an approach based on screw theory and line geometry for the flank milling of dually defined twisted ruled surfaces. The designed surface is defined by a single-parametric dual nonuniform rational basis spline representation, while the tool’s axis is represented by a dual unit vector. The machining is performed along the dually defined lines and not per point since the ruled surface is represented by an aggregate of lines. The initial locating of the tool is accomplished via dual vector algebra and line geometry. Our method results in compact algorithms and fast tool-position calculation due to the single-parametric definition of the ruled surface and to the dual orthogonal matrix operator that is utilized to spatially associate the tool and the surface. The tool path determination is based on the offset of the designed surface. An iterative algorithm is introduced to ensure interference-free tool path that eliminates overcut. The introduced approach can be applied to twisted ruled surfaces and is appropriate for the machining of blades, propellers and turbines.",
url = "http://pib.sagepub.com/content/228/3/356.abstract",
eprint = "http://pib.sagepub.com/content/228/3/356.full.pdf+html",
journal = "Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture"
}

Panagiotis N Koustoumpardis and Nikos A Aspragathos. Intelligent hierarchical robot control for sewing fabrics. Robotics and Computer-Integrated Manufacturing 30(1):34 - 46, 2014. URL, AbstractAbstract In this paper an intelligent hierarchical controller for the robotized sewing of two plies of fabrics is presented. The proposed system is based on the concept: fabric properties estimation – tensional force determination – sewing – adaptation. A new methodology for integrating the tensile test of fabrics into the robotic sewing station using the sewing machine is presented. The output of this test is the estimation of the fabrics extensibility, which is fed to the next level of decision making to determine the appropriate fabric tensional force that should be applied during the sewing process. Computational intelligence methods (fuzzy logic and neural networks) have been used throughout the hierarchical structure of the controller. The present research is focused on the concept of using qualitative properties of the fabrics and the processing of qualitative and quantitative knowledge in different levels of the introduced hierarchical system. The proposed system is flexible, adaptable and robust enough to sew a wide range of unknown double ply of fabrics as it is shown by the test results. It has also the capability of on-line and endless training in order to be able to respond, handle and sew new types of fabrics. Seams that are produced by the robot and a human operator for joining two pieces of fabrics are presented and compared.BibTeX

@article{Koustoumpardis201434,
title = "Intelligent hierarchical robot control for sewing fabrics",
journal = "Robotics and Computer-Integrated Manufacturing",
volume = 30,
number = 1,
pages = "34 - 46",
year = 2014,
note = "",
issn = "0736-5845",
doi = "http://dx.doi.org/10.1016/j.rcim.2013.08.001",
url = "http://www.sciencedirect.com/science/article/pii/S0736584513000574",
author = "Panagiotis N. Koustoumpardis and Nikos A. Aspragathos",
abstract = "Abstract In this paper an intelligent hierarchical controller for the robotized sewing of two plies of fabrics is presented. The proposed system is based on the concept: fabric properties estimation – tensional force determination – sewing – adaptation. A new methodology for integrating the tensile test of fabrics into the robotic sewing station using the sewing machine is presented. The output of this test is the estimation of the fabrics extensibility, which is fed to the next level of decision making to determine the appropriate fabric tensional force that should be applied during the sewing process. Computational intelligence methods (fuzzy logic and neural networks) have been used throughout the hierarchical structure of the controller. The present research is focused on the concept of using qualitative properties of the fabrics and the processing of qualitative and quantitative knowledge in different levels of the introduced hierarchical system. The proposed system is flexible, adaptable and robust enough to sew a wide range of unknown double ply of fabrics as it is shown by the test results. It has also the capability of on-line and endless training in order to be able to respond, handle and sew new types of fabrics. Seams that are produced by the robot and a human operator for joining two pieces of fabrics are presented and compared."
}

Nikos A Aspragathos. Commons-based Science and Research and the Privatization of its Fruits: The Robotics Paradigm. Journal of Innovation Economics 2(12), 2013. BibTeX

Paraskevi Th. Zacharia, Elias K Xidias and Nikos A Aspragathos. Task scheduling and motion planning for an industrial manipulator. Robotics and Computer-Integrated Manufacturing 29(6):449 - 462, 2013. URL, AbstractIn many robotic industrial applications, a manipulator should move among obstacles and reach a set of task-points in order to perform a pre-defined task. It is quite important as well as very complicated to determine the time-optimum sequence of the task-points visited by the end-effector's tip only once assuring that the manipulator's motion through the successive task-points is collision-free. This paper introduces a method for simultaneously planning collision-free motion and scheduling time-optimal route along a set of given task-points. This method is based on the projection of the workspace and the robot on the B-Surface to formulate an objective function for the minimization of the cycle time in visiting multiple task-points and taken into account the multiple solutions of the inverse kinematics and the obstacle avoidance. A modified GA with special encoding to encounter the multiplicity of the robot inverse kinematics and the required intermediate configurations is used for the searching of the optimal solution on the B-Surface. The simulation results show the efficiency and the effectiveness of the proposed approach to determine a suboptimal tour for multi-goal motion planning in complex environments cluttered with obstacles.BibTeX

@article{Zach13,
title = "Task scheduling and motion planning for an industrial manipulator",
journal = "Robotics and Computer-Integrated Manufacturing",
volume = 29,
number = 6,
pages = "449 - 462",
year = 2013,
issn = "0736-5845",
doi = "http://dx.doi.org/10.1016/j.rcim.2013.05.002",
url = "http://www.sciencedirect.com/science/article/pii/S0736584513000410",
author = "Paraskevi Th. Zacharia and Elias K. Xidias and Nikos A. Aspragathos",
abstract = "In many robotic industrial applications, a manipulator should move among obstacles and reach a set of task-points in order to perform a pre-defined task. It is quite important as well as very complicated to determine the time-optimum sequence of the task-points visited by the end-effector's tip only once assuring that the manipulator's motion through the successive task-points is collision-free. This paper introduces a method for simultaneously planning collision-free motion and scheduling time-optimal route along a set of given task-points. This method is based on the projection of the workspace and the robot on the B-Surface to formulate an objective function for the minimization of the cycle time in visiting multiple task-points and taken into account the multiple solutions of the inverse kinematics and the obstacle avoidance. A modified GA with special encoding to encounter the multiplicity of the robot inverse kinematics and the required intermediate configurations is used for the searching of the optimal solution on the B-Surface. The simulation results show the efficiency and the effectiveness of the proposed approach to determine a suboptimal tour for multi-goal motion planning in complex environments cluttered with obstacles."
}

Fotios Dimeas, Panagiotis Koustoumpardis and Nikos Aspragathos. Admittance neuro-control of a lifting device to reduce human effort. Advanced Robotics 27(13):1013–1022, June 2013. URL, AbstractIn this paper, two admittance-based control schemes for a power-assisted lifting device are presented. This device can be used to hoist a heavy object interactively for reducing the operator¢'s burden. The proposed system integrates an admittance controller with an inner control loop that regulates the velocity of the object. The admittance is the outer loop that establishes the desired relation between the applied force to the object and its velocity. For the adaptation to a variety of loads, an online learning controller is implemented based on a neural network (NN) with backpropagation training. The overfitting of the NN is resolved with weight decay to decrease the oscillations around the equilibrium point. Alternatively, a gain scheduling PID controller is designed for the inner loop, which measures the object weight and tunes the gains with predefined rules. The performance of these two adaptation methods is demonstrated on an experimental setup and the results illustrate that better generalization can be achieved with the NN.BibTeX

@article{dim2013,
author = "Dimeas, Fotios and Koustoumpardis, Panagiotis and Aspragathos, Nikos",
doi = "10.1080/01691864.2013.804801",
issn = "0169-1864",
journal = "Advanced Robotics",
keywords = "admittance,neurocontrol,pid,power assist",
month = "jun",
number = 13,
pages = "1013--1022",
title = "{Admittance neuro-control of a lifting device to reduce human effort}",
url = "http://www.tandfonline.com/doi/abs/10.1080/01691864.2013.804801",
volume = 27,
year = 2013,
abstract = "In this paper, two admittance-based control schemes for a power-assisted lifting device are presented. This device can be used to hoist a heavy object interactively for reducing the operator¢'s burden. The proposed system integrates an admittance controller with an inner control loop that regulates the velocity of the object. The admittance is the outer loop that establishes the desired relation between the applied force to the object and its velocity. For the adaptation to a variety of loads, an online learning controller is implemented based on a neural network (NN) with backpropagation training. The overfitting of the NN is resolved with weight decay to decrease the oscillations around the equilibrium point. Alternatively, a gain scheduling PID controller is designed for the inner loop, which measures the object weight and tunes the gains with predefined rules. The performance of these two adaptation methods is demonstrated on an experimental setup and the results illustrate that better generalization can be achieved with the NN."
}

Charalampos Valsamos, Vassilis Moulianitis and Nikos Aspragathos. Index based optimal anatomy of a metamorphic manipulator for a given task. Robotics and Computer-Integrated Manufacturing 28(4):517 - 529, 2012. URL, AbstractThis paper introduces an approach for the determination of the best anatomy of a metamorphic manipulator for a given task at a given location. The location of the task is determined by maximizing the performance of a current industrial fixed anatomy robot. Two types of tasks are considered: a point to point task and a path following task, where in the first case the approximated minimum of the manipulability index is formed along the task points and in the second case the approximated minimum of the manipulator velocity ratio is formed along the line segments. These indexes are maximized in order to determine the best anatomy for the task. The proposed approach is tested and the results show that the determined best anatomy for each type of task acquired higher performance than the respective one achieved by the fixed anatomy manipulator.BibTeX

@article{val12b,
title = "Index based optimal anatomy of a metamorphic manipulator for a given task",
journal = "Robotics and Computer-Integrated Manufacturing",
volume = 28,
number = 4,
pages = "517 - 529",
year = 2012,
issn = "0736-5845",
doi = "http://dx.doi.org/10.1016/j.rcim.2011.11.006",
url = "http://www.sciencedirect.com/science/article/pii/S0736584511001384",
author = "Charalampos Valsamos and Vassilis Moulianitis and Nikos Aspragathos",
keywords = "Product of exponentials formula",
abstract = "This paper introduces an approach for the determination of the best anatomy of a metamorphic manipulator for a given task at a given location. The location of the task is determined by maximizing the performance of a current industrial fixed anatomy robot. Two types of tasks are considered: a point to point task and a path following task, where in the first case the approximated minimum of the manipulability index is formed along the task points and in the second case the approximated minimum of the manipulator velocity ratio is formed along the line segments. These indexes are maximized in order to determine the best anatomy for the task. The proposed approach is tested and the results show that the determined best anatomy for each type of task acquired higher performance than the respective one achieved by the fixed anatomy manipulator."
}

Elias K Xidias, Andreas C Nearchou and Nikos A Aspragathos. Integrating path planning, routing and scheduling for logistics operations in manufacturing facilities. Cybernetics and Systems 43(3):143-162, 2012. URL, AbstractThis article considers the following manufacturing/logistics problem: an autonomous vehicle (AV) is requested to serve a set of pickup and delivery (P/D) stations in the shop floor of a modern factory providing P/D tasks while moving safely (i.e., avoiding any collision with obstacles) in its environment. A two-sided time window associated with each P/D station brackets the service time to within a specified interval. A tour for AV is considered legal if it (a) is collision free, (b) passes through each P/D station exactly once, and (c) satisfies the service time restrictions imposed by the P/D stations. A legal tour always starts and ends at a depot. The problem is thereby dual NP-hard because it combines the characteristics of path planning and those of vehicle routing and scheduling problems. The objective is to determine the shortest possible legal tour for AV. A new method is introduced to solve the problem accomplished in two successive phases: first, AV's environment is mapped into a 2D B-spline surface embedded in 3D Euclidean space using a robust geometric model. Then, the generated surface is searched using a genetic algorithm for an optimum legal tour that satisfies the requirements of the vehicle's mission. The performance of the proposed method is investigated and discussed through characteristic simulated experiments.BibTeX

@article{xidi12,
author = "Xidias, Elias K. and Nearchou, Andreas C. and Aspragathos, Nikos A.",
title = "Integrating path planning, routing and scheduling for logistics operations in manufacturing facilities",
journal = "Cybernetics and Systems",
volume = 43,
number = 3,
pages = "143-162",
year = 2012,
doi = "10.1080/01969722.2012.659965",
url = "http://www.tandfonline.com/doi/abs/10.1080/01969722.2012.659965",
eprint = "http://www.tandfonline.com/doi/pdf/10.1080/01969722.2012.659965",
abstract = "This article considers the following manufacturing/logistics problem: an autonomous vehicle (AV) is requested to serve a set of pickup and delivery (P/D) stations in the shop floor of a modern factory providing P/D tasks while moving safely (i.e., avoiding any collision with obstacles) in its environment. A two-sided time window associated with each P/D station brackets the service time to within a specified interval. A tour for AV is considered legal if it (a) is collision free, (b) passes through each P/D station exactly once, and (c) satisfies the service time restrictions imposed by the P/D stations. A legal tour always starts and ends at a depot. The problem is thereby dual NP-hard because it combines the characteristics of path planning and those of vehicle routing and scheduling problems. The objective is to determine the shortest possible legal tour for AV. A new method is introduced to solve the problem accomplished in two successive phases: first, AV's environment is mapped into a 2D B-spline surface embedded in 3D Euclidean space using a robust geometric model. Then, the generated surface is searched using a genetic algorithm for an optimum legal tour that satisfies the requirements of the vehicle's mission. The performance of the proposed method is investigated and discussed through characteristic simulated experiments."
}

P Lazarou, N Aspragathos and J Wilde. Modelling, simulation and design constraints of electrostatic self-assembly of microparts. Journal of Manufacturing Science and Technology 4(4):401 - 407, 2011. URL, AbstractSelf-assembly is a technique that involves the manipulation and alignment of microparts onto a substrate without additional machinery and makes it possible to assemble a large number of small devices in parallel. A novel concept for the self-alignment of microparts on a substrate by means of electrostatic attraction has been previously introduced and experimentally verified by the authors. In this paper FE modelling is used to determine the magnitude of the self-aligning force and from these findings, a semi-empirical, fitted force model is produced for circular, complementary electrodes between micropart and substrate. Based on this force model, constraints useful for the design and the prediction of the behaviour of microparts are proposed and dynamic simulations of the alignment procedure are presented. The results of these simulations and the previously conducted experiments, as well as the introduced design constraints are the first steps towards the modelling and the implementation of a parallel assembly approach of tiny parts and thereby integration of heterogeneous materials.BibTeX

@article{laza11,
title = "Modelling, simulation and design constraints of electrostatic self-assembly of microparts",
journal = "Journal of Manufacturing Science and Technology",
volume = 4,
number = 4,
pages = "401 - 407",
year = 2011,
note = "Special Issue on Micro Manufacturing based on the 2009 4M ICOMM Conference",
issn = "1755-5817",
doi = "http://dx.doi.org/10.1016/j.cirpj.2011.03.004",
url = "http://www.sciencedirect.com/science/article/pii/S1755581711000356",
author = "P. Lazarou and N. Aspragathos and J. Wilde",
abstract = "Self-assembly is a technique that involves the manipulation and alignment of microparts onto a substrate without additional machinery and makes it possible to assemble a large number of small devices in parallel. A novel concept for the self-alignment of microparts on a substrate by means of electrostatic attraction has been previously introduced and experimentally verified by the authors. In this paper FE modelling is used to determine the magnitude of the self-aligning force and from these findings, a semi-empirical, fitted force model is produced for circular, complementary electrodes between micropart and substrate. Based on this force model, constraints useful for the design and the prediction of the behaviour of microparts are proposed and dynamic simulations of the alignment procedure are presented. The results of these simulations and the previously conducted experiments, as well as the introduced design constraints are the first steps towards the modelling and the implementation of a parallel assembly approach of tiny parts and thereby integration of heterogeneous materials."
}

Panagiotis Sotiropoulos, Nikos Aspragathos and F Andritsos. Optimum docking of an Unmanned Underwater Vehicle for high dexterity manipulation. IAENG International Journal of Computer Science 38(1):48-56, 2011. URL, AbstractA method for the determination of the optimum docking or hovering position of an Underwater Unmanned Vehicle is proposed for performing a desired intervention task with high dexterity. The optimization problem is formulated taken into account primarily the manipulator's dexterity in the area of intervention as well as the distance between the current position and the optimal one and the geometric constraints imposed by the environment. A Genetic Algorithm is designed and implemented to search for the best docking position. An underwater scenario with a UUV equipped with a 6 DOF manipulator is examined in order to verify the applicability of the proposed approach.BibTeX

@article{sotir11,
author = "Sotiropoulos, Panagiotis and Aspragathos, Nikos and Andritsos, F.",
title = "Optimum docking of an Unmanned Underwater Vehicle for high dexterity manipulation",
journal = "IAENG International Journal of Computer Science",
year = 2011,
volume = 38,
number = 1,
pages = "48-56",
note = "cited By (since 1996)3",
url = "http://www.scopus.com/inward/record.url?eid=2-s2.0-79951735296&partnerID=40&md5=7dc809980cd55434f5e0fde2b9053d4b",
affiliation = "The European Commission, Joint Research Centre, Ispra, VA 21027, Italy; Mechanical Engineering and Aeronautics Department, University of Patras, Patras 26500, Greece",
abstract = "A method for the determination of the optimum docking or hovering position of an Underwater Unmanned Vehicle is proposed for performing a desired intervention task with high dexterity. The optimization problem is formulated taken into account primarily the manipulator's dexterity in the area of intervention as well as the distance between the current position and the optimal one and the geometric constraints imposed by the environment. A Genetic Algorithm is designed and implemented to search for the best docking position. An underwater scenario with a UUV equipped with a 6 DOF manipulator is examined in order to verify the applicability of the proposed approach."
}

Johan Dalin, Jurgen Wilde, Panos Lazarou and Nikolaos Aspragathos. Self-assembly of dies through electrostatic attraction: modelling of alignment forces and kinematics. Journal of Micro-Nano Mechatronics 6(1-2):23-31, 2011. URL, AbstractA variety of self-assembly procedures have been introduced. An interesting and prospective application of this technology is the manufacturing of heterogeneously integrated electronic circuits. The two main approaches are top-down and bottom-up self-assembly. Top-down self-assembly is a massively parallel approach for assembly and alignment of small but highly functional parts onto a substrate without using additional machinery. This paper discusses a concept where electrostatic forces are used to achieve top-down self-alignment of parts in the micro- and milli scale. This approach is also concievable to accomplish accurate alignment of pre-positioned dies, for example electronic integrated circuits. For this approach complementary and electrically conductive micro-structured patterns serve as alignment structures. Experimental results have verified that it is feasible to accomplish self-assembly and accurate alignment of single micro-structured parts. The alignment forces and kinematics for parts in the range of a few hundred micrometers have been modelled and computed, respectively. Simulations have been performed in Matlab/Simulink. The presented simulation tool along with the experimental results is the first steps towards the modelling and the realisation of a massively parallel assembly approach of dies.BibTeX

@article{dalin11,
year = 2011,
issn = "1865-3928",
journal = "Journal of Micro-Nano Mechatronics",
volume = 6,
number = "1-2",
doi = "10.1007/s12213-010-0031-4",
title = "Self-assembly of dies through electrostatic attraction: modelling of alignment forces and kinematics",
url = "http://dx.doi.org/10.1007/s12213-010-0031-4",
publisher = "Springer-Verlag",
keywords = "Electrostatic self-assembly; Hybrid integrated circuits; Accurate die alignment",
author = "Dalin, Johan and Wilde, Jurgen and Lazarou, Panos and Aspragathos, Nikolaos",
pages = "23-31",
abstract = "A variety of self-assembly procedures have been introduced. An interesting and prospective application of this technology is the manufacturing of heterogeneously integrated electronic circuits. The two main approaches are top-down and bottom-up self-assembly. Top-down self-assembly is a massively parallel approach for assembly and alignment of small but highly functional parts onto a substrate without using additional machinery. This paper discusses a concept where electrostatic forces are used to achieve top-down self-alignment of parts in the micro- and milli scale. This approach is also concievable to accomplish accurate alignment of pre-positioned dies, for example electronic integrated circuits. For this approach complementary and electrically conductive micro-structured patterns serve as alignment structures. Experimental results have verified that it is feasible to accomplish self-assembly and accurate alignment of single micro-structured parts. The alignment forces and kinematics for parts in the range of a few hundred micrometers have been modelled and computed, respectively. Simulations have been performed in Matlab/Simulink. The presented simulation tool along with the experimental results is the first steps towards the modelling and the realisation of a massively parallel assembly approach of dies.",
language = "English"
}

V C Moulianitis and N A Aspragathos. Introduction to the special issue on Theories and Methodologies for mechatronics design. Mechatronics 20(8):825 - 826, 2010. URL, AbstractBibTeX

E K Xidias, Th. P Zacharia and N A Aspragathos. Time-optimal task scheduling for articulated manipulators in environments cluttered with obstacles. Robotica 28:427–440, May 2010. URL, AbstractABSTRACT SUMMARYThis paper proposes a new approach for solving a generalization of the task scheduling problem for articulated robots (either redundant or non-redundant), where the robot's 2D environment is cluttered with obstacles of arbitrary size, shape and location, while a set of task-points are located in the robot's free-space. The objective is to determine the optimum collision-free robot's tip tour through all task-points passing from each one exactly once and returning to the initial task-point. This scheduling problem combines two computationally NP-hard problems: the optimal scheduling of robot tasks and the collision-free motion planning between the task-points.The proposed approach employs the bump-surface (B-Surface) concept for the representation of the 2D robot's environment by a B-Spline surface embedded in 3D Euclidean space. The time-optimal task scheduling is being searched on the generated B-Surface using a genetic algorithm (GA) with a special encoding in order to take into consideration the infinite configurations corresponding to each task-point. The result of the GA's searching constitutes the solution to the task scheduling problem and satisfies optimally the task scheduling criteria and objectives. Extensive experimental results show the efficiency and the effectiveness of the proposed method to determine the collision-free motion among obstacles.BibTeX

@article{ROB:7408560,
author = "Xidias,E. K. and Zacharia,P. Th. and Aspragathos,N. A.",
title = "Time-optimal task scheduling for articulated manipulators in environments cluttered with obstacles",
journal = "Robotica",
volume = 28,
issue = 03,
month = 5,
year = 2010,
issn = "1469-8668",
pages = "427--440",
numpages = 14,
doi = "10.1017/S0263574709005748",
url = "http://journals.cambridge.org/article_S0263574709005748",
abstract = "ABSTRACT SUMMARYThis paper proposes a new approach for solving a generalization of the task scheduling problem for articulated robots (either redundant or non-redundant), where the robot's 2D environment is cluttered with obstacles of arbitrary size, shape and location, while a set of task-points are located in the robot's free-space. The objective is to determine the optimum collision-free robot's tip tour through all task-points passing from each one exactly once and returning to the initial task-point. This scheduling problem combines two computationally NP-hard problems: the optimal scheduling of robot tasks and the collision-free motion planning between the task-points.The proposed approach employs the bump-surface (B-Surface) concept for the representation of the 2D robot's environment by a B-Spline surface embedded in 3D Euclidean space. The time-optimal task scheduling is being searched on the generated B-Surface using a genetic algorithm (GA) with a special encoding in order to take into consideration the infinite configurations corresponding to each task-point. The result of the GA's searching constitutes the solution to the task scheduling problem and satisfies optimally the task scheduling criteria and objectives. Extensive experimental results show the efficiency and the effectiveness of the proposed method to determine the collision-free motion among obstacles."
}

Athanasios Nektarios and Nikos A Aspragathos. Optimal location of a general position and orientation end-effector's path relative to manipulator's base, considering velocity performance. Robotics and Computer-Integrated Manufacturing 26(2):162 - 173, 2010. URL, AbstractThe objective of the present paper is to introduce an offline algorithm searching for the optimal or suboptimal placement of a robot's base during workcell design, so that its end-effector can perform a position and orientation path following task of a given 3D curved path and orientation, maximizing the manipulator's velocity performance. The global index employed for this velocity performance optimization is the approximation of the minimum manipulator velocity ratio (AMMVR). The AMMVR is computed from a finite set of MVR values computed at specific locations along the path selected by a trajectory approximation algorithm. This algorithm approximates the path using an interpolation method based on the cubic spline interpolation to guarantee velocity continuity. The optimization is performed by a simple genetic algorithm, using as fitness function the AMMVR and the manipulator's constraints. The algorithm's effectiveness is demonstrated by simulation tests using a six-degree-of-freedom non-redundant Puma type manipulator and the obtained results are presented and discussed.BibTeX

@article{Nektarios2010162,
title = "Optimal location of a general position and orientation end-effector's path relative to manipulator's base, considering velocity performance",
journal = "Robotics and Computer-Integrated Manufacturing",
volume = 26,
number = 2,
pages = "162 - 173",
year = 2010,
note = "",
issn = "0736-5845",
doi = "http://dx.doi.org/10.1016/j.rcim.2009.07.003",
url = "http://www.sciencedirect.com/science/article/pii/S0736584509000623",
author = "Athanasios Nektarios and Nikos A. Aspragathos",
keywords = "Workcell design",
abstract = "The objective of the present paper is to introduce an offline algorithm searching for the optimal or suboptimal placement of a robot's base during workcell design, so that its end-effector can perform a position and orientation path following task of a given 3D curved path and orientation, maximizing the manipulator's velocity performance. The global index employed for this velocity performance optimization is the approximation of the minimum manipulator velocity ratio (AMMVR). The \{AMMVR\} is computed from a finite set of \{MVR\} values computed at specific locations along the path selected by a trajectory approximation algorithm. This algorithm approximates the path using an interpolation method based on the cubic spline interpolation to guarantee velocity continuity. The optimization is performed by a simple genetic algorithm, using as fitness function the \{AMMVR\} and the manipulator's constraints. The algorithm's effectiveness is demonstrated by simulation tests using a six-degree-of-freedom non-redundant Puma type manipulator and the obtained results are presented and discussed."
}

Johan Dalin, Jurgen Wilde, Azeem Zulfiqar, Panos Lazarou, Aris Synodinos and Nikolaos Aspragathos. Electrostatic attraction and surface-tension-driven forces for accurate self-assembly of microparts. Microelectronic Engineering 87(2):159 - 162, 2010. URL, AbstractSelf-assembly is not widely used in industrial micro-fabrication, although it can potentially involve assembly processes that are considerably less complex. A variety of procedures for self-alignment of parts have been introduced and investigated lately. These procedures mainly utilise capillary, gravitational or electrostatic forces in the micro-scale. This paper investigates two different concepts for accurate self-assembly of parts. One is well described in the literature by third parties and involves the alignment of parts by utilising the surface tensions of micro-scaled adhesive films, which are selectively coated on hydrophobic alignment structures. In the present publication the influence of the dimensions of such structured alignment sites on the process flow is discussed. The second concept is a novel approach to accomplish self-alignment of micro-structures with electrostatic attraction. Several complementary and electrically conductive micro-structured patterns serve as binding sites for the alignment of parts in this approach. In order to obtain knowledge of how these two approaches operate, they have been modelled and simulated. Additionally, in order to analyse the feasibility of these procedures and to verify simulation results experiments have been performed on micro-structured parts and substrates. In particular, the layout of the alignment structures and the size of the parts were identical for both described concepts in the experimental work; therefore, these two methods were compared. With the self-assembly procedure that utilises electrostatic attraction, high alignment accuracies and forces, affecting the part over large distances, were observed. Finally, parts with micro-structured binding sites, which were as small as 10 Γ— 10 ΞΌm2, could accurately be self-aligned with electrostatic attraction.BibTeX

@article{Dalin2010159,
title = "Electrostatic attraction and surface-tension-driven forces for accurate self-assembly of microparts",
journal = "Microelectronic Engineering",
volume = 87,
number = 2,
pages = "159 - 162",
year = 2010,
note = "",
issn = "0167-9317",
doi = "http://dx.doi.org/10.1016/j.mee.2009.06.033",
url = "http://www.sciencedirect.com/science/article/pii/S0167931709004912",
author = "Johan Dalin and Jurgen Wilde and Azeem Zulfiqar and Panos Lazarou and Aris Synodinos and Nikolaos Aspragathos",
keywords = "Electrostatic forces",
abstract = "Self-assembly is not widely used in industrial micro-fabrication, although it can potentially involve assembly processes that are considerably less complex. A variety of procedures for self-alignment of parts have been introduced and investigated lately. These procedures mainly utilise capillary, gravitational or electrostatic forces in the micro-scale. This paper investigates two different concepts for accurate self-assembly of parts. One is well described in the literature by third parties and involves the alignment of parts by utilising the surface tensions of micro-scaled adhesive films, which are selectively coated on hydrophobic alignment structures. In the present publication the influence of the dimensions of such structured alignment sites on the process flow is discussed. The second concept is a novel approach to accomplish self-alignment of micro-structures with electrostatic attraction. Several complementary and electrically conductive micro-structured patterns serve as binding sites for the alignment of parts in this approach. In order to obtain knowledge of how these two approaches operate, they have been modelled and simulated. Additionally, in order to analyse the feasibility of these procedures and to verify simulation results experiments have been performed on micro-structured parts and substrates. In particular, the layout of the alignment structures and the size of the parts were identical for both described concepts in the experimental work; therefore, these two methods were compared. With the self-assembly procedure that utilises electrostatic attraction, high alignment accuracies and forces, affecting the part over large distances, were observed. Finally, parts with micro-structured binding sites, which were as small as 10 Γ— 10 ΞΌm2, could accurately be self-aligned with electrostatic attraction."
}

EK Xidias, Th P Zacharia and NA Aspragathos. Time-optimal task scheduling for two robotic manipulators operating in a three-dimensional environment. Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering 224(7):845–855, 2010. BibTeX

G T Zoumponos and N A Aspragathos. A fuzzy strategy for the robotic folding of fabrics with machine vision feedback. Industrial Robot 37(3):302-308, 2010. URL, AbstractPurpose - Some areas of the apparel industry, such as folding and sewing, are still labor intensive. The purpose of this paper is to present a new fuzzy visual servoing strategy for the folding of fabric strips by robotic manipulators. Design/methodology/approach - Three stages of the folding task are distinguished experimentally, the initial laying, the true folding, and the final laying. An indirect visual servoing fuzzy system, employing two cameras, is developed to guide the robot along each of the stages. Findings - The proposed scheme manages to successfully fold some of the tested materials. The experimental results are promising and well within the limitations posed by both the employed equipment and the nature of the handled materials. Research limitations/implications - This study is limited to rectangular strips of fabrics and does not consider the speed of the process. Practical implications - The resulting system provides a stepping stone for the introduction of automation to currently labor-intensive areas of the apparel industry. Originality/value - The separate folding stages reduce the complexity of the overall system and the introduced visually extracted features allow a closer monitoring of the process.BibTeX

@article{Zoumponos2010302,
author = "Zoumponos, G.T. and Aspragathos, N.A.",
title = "A fuzzy strategy for the robotic folding of fabrics with machine vision feedback",
journal = "Industrial Robot",
year = 2010,
volume = 37,
number = 3,
pages = "302-308",
note = "cited By (since 1996)1",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-77951898664&partnerID=40&md5=45350a8053770007f33ecba076502569",
affiliation = "Mechanical and Aeronautics Engineering Department, University of Patras, Patra, Greece",
abstract = "Purpose - Some areas of the apparel industry, such as folding and sewing, are still labor intensive. The purpose of this paper is to present a new fuzzy visual servoing strategy for the folding of fabric strips by robotic manipulators. Design/methodology/approach - Three stages of the folding task are distinguished experimentally, the initial laying, the true folding, and the final laying. An indirect visual servoing fuzzy system, employing two cameras, is developed to guide the robot along each of the stages. Findings - The proposed scheme manages to successfully fold some of the tested materials. The experimental results are promising and well within the limitations posed by both the employed equipment and the nature of the handled materials. Research limitations/implications - This study is limited to rectangular strips of fabrics and does not consider the speed of the process. Practical implications - The resulting system provides a stepping stone for the introduction of automation to currently labor-intensive areas of the apparel industry. Originality/value - The separate folding stages reduce the complexity of the overall system and the introduced visually extracted features allow a closer monitoring of the process."
}

P Zacharia, N Aspragathos, I Mariolis and E Dermatas. A robotic system based on fuzzy visual servoing for handling flexible sheets lying on a table. Industrial Robot 36(5):489-496, 2009. URL, AbstractPurpose - The purpose of this paper is to present a flexible automation system for the manipulation of fabrics lying on a work table and focuses on the design of a robot control system based on visual servoing and fuzzy logic for handling flexible sheets lying on a table. The main contribution of this paper is that the developed system tolerates deformations that may appear during robot handling of fabrics due to buckling without the need for fabric rigidization. Design/methodology/approach - The vision system, consisting of two cameras, extracts the features that are necessary for handling the fabric despite possible deformations or occlusion from the robotic arm. An intelligent controller based on visual servoing is implemented enabling the robot to handle a variety of fabrics without the need for a mathematical model or complex mathematical/geometrical computations. To enhance its performance, the conventional fuzzy logic controller is tuned through genetic algorithms and an adaptation mechanism and the respective performance is evaluated. The experiments show that the proposed robotic system is flexible enough to handle various fabrics and robust in handling deformations that may change fabric's shape due to buckling. Findings - The experiments show that the proposed robotic system is flexible enough to handle various fabrics and robust in handling deformations that may change fabric's shape due to buckling. Research limitations/implications - It is not possible to cover all the aspects of robot handling of flexible materials in this paper, since there are still several related issues requiring solutions. Considering the future research work, the proposed approach can be extended to sew fabrics with curved edges and correcting the distortions presented during robot handling of fabrics. Practical implications - The paper includes implications for robot handling a variety of fabrics with low and medium bending rigidity on a working table. The intent of this paper deals with buckling in context of achieving a successful seam tracking and not the correction strategy against folding or wrinkling problems. Originality/value - This paper fulfils an identified need to study the fabrics' behavior towards robot handling on a working table.BibTeX

@article{Zacharia2009489,
author = "Zacharia, P. and Aspragathos, N. and Mariolis, I. and Dermatas, E.",
title = "A robotic system based on fuzzy visual servoing for handling flexible sheets lying on a table",
journal = "Industrial Robot",
year = 2009,
volume = 36,
number = 5,
pages = "489-496",
note = "cited By (since 1996)3",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-70249096311&partnerID=40&md5=b519232e87a34f0a845862621be3a16a",
affiliation = "Department of Mechanical and Aeronautics Engineering, University of Patras, Patras, Greece",
abstract = "Purpose - The purpose of this paper is to present a flexible automation system for the manipulation of fabrics lying on a work table and focuses on the design of a robot control system based on visual servoing and fuzzy logic for handling flexible sheets lying on a table. The main contribution of this paper is that the developed system tolerates deformations that may appear during robot handling of fabrics due to buckling without the need for fabric rigidization. Design/methodology/approach - The vision system, consisting of two cameras, extracts the features that are necessary for handling the fabric despite possible deformations or occlusion from the robotic arm. An intelligent controller based on visual servoing is implemented enabling the robot to handle a variety of fabrics without the need for a mathematical model or complex mathematical/geometrical computations. To enhance its performance, the conventional fuzzy logic controller is tuned through genetic algorithms and an adaptation mechanism and the respective performance is evaluated. The experiments show that the proposed robotic system is flexible enough to handle various fabrics and robust in handling deformations that may change fabric's shape due to buckling. Findings - The experiments show that the proposed robotic system is flexible enough to handle various fabrics and robust in handling deformations that may change fabric's shape due to buckling. Research limitations/implications - It is not possible to cover all the aspects of robot handling of flexible materials in this paper, since there are still several related issues requiring solutions. Considering the future research work, the proposed approach can be extended to sew fabrics with curved edges and correcting the distortions presented during robot handling of fabrics. Practical implications - The paper includes implications for robot handling a variety of fabrics with low and medium bending rigidity on a working table. The intent of this paper deals with buckling in context of achieving a successful seam tracking and not the correction strategy against folding or wrinkling problems. Originality/value - This paper fulfils an identified need to study the fabrics' behavior towards robot handling on a working table."
}

P Lazarou and N A Aspragathos. An integrated mechatronic approach for the systematic design of force fields and programming of microactuator arrays for micropart manipulation. Mechatronics 19(3):287-303, 2009. URL, AbstractMicromanipulation is a hot topic in the rapidly emerging area of micromechatronics and particularly in the manufacturing and assembling of micromechatronic products. This paper introduces an integrated mechatronic approach for the systematic design and operation of flexible, sensorless, automated micromanipulation for a variety of microparts on microactuation arrays. This approach is a mechatronic synthesis of methods from different engineering areas such as solid modeling, electronics design, software for control and programming of mechanical actuation. It involves designing of programmable force fields for manipulation of convex or non-convex polygonal microparts on an array, hardware programmable circuitry for the activation of the array and a software algorithmic procedure for the programming. A detailed analysis is given, as well as several simulated experiments performed using the introduced approach on a cilia microactuator array for a variety of polygonal asymmetric and non-convex microparts and the results are presented and discussed. Finally, the advantages and limitations of this approach are analyzed and points for further research are raised.BibTeX

@article{Lazarou2009287,
author = "Lazarou, P. and Aspragathos, N.A.",
title = "An integrated mechatronic approach for the systematic design of force fields and programming of microactuator arrays for micropart manipulation",
journal = "Mechatronics",
year = 2009,
volume = 19,
number = 3,
pages = "287-303",
note = "cited By (since 1996)1",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-62549129443&partnerID=40&md5=35972a45585506fbbd0e130df25930df",
affiliation = "Robotics Group, Department of Mechanical Engineering and Aeronautics, University of Patras, Rion, Patras, T.K. 26500, Greece",
abstract = "Micromanipulation is a hot topic in the rapidly emerging area of micromechatronics and particularly in the manufacturing and assembling of micromechatronic products. This paper introduces an integrated mechatronic approach for the systematic design and operation of flexible, sensorless, automated micromanipulation for a variety of microparts on microactuation arrays. This approach is a mechatronic synthesis of methods from different engineering areas such as solid modeling, electronics design, software for control and programming of mechanical actuation. It involves designing of programmable force fields for manipulation of convex or non-convex polygonal microparts on an array, hardware programmable circuitry for the activation of the array and a software algorithmic procedure for the programming. A detailed analysis is given, as well as several simulated experiments performed using the introduced approach on a cilia microactuator array for a variety of polygonal asymmetric and non-convex microparts and the results are presented and discussed. Finally, the advantages and limitations of this approach are analyzed and points for further research are raised."
}

E K Xidias, A C Nearchou and N A Aspragathos. Vehicle scheduling in 2D shop floor environments. Industrial Robot 36(2):176-183, 2009. URL, AbstractPurpose - The purpose of this paper is to develop an efficient method for solving a vehicle scheduling problem (VSP) in 2D industrial environments. An autonomous vehicle is requested to serve a set of work centers in the shop floor providing transport and delivery tasks while avoiding collisions with obstacles during its travel. The objective is to find a minimum in length, collision-free vehicle routing schedule that serves timely as many as possible work centers in the shop floor. Design/methodology/approach - First, the vehicle's environment is mapped into a 2D B-Spline surface embedded in 3D Euclidean space using a robust geometric model. Then, a modified genetic algorithm is applied on the generated surface to search for an optimum legal route schedule that satisfies the requirements of the vehicle's mission. Findings - Simulation experiments show that the method is robust enough and can determine in a reasonable computation time a solution to VSP under consideration. Originality/value - There is a gap in the literature for methods that face VSP in shop-floor environments. This paper contributes to filling this gap by implementing a practical method that can be easily programmed and included in a modern service delivery system.BibTeX

@article{Xidias2009176,
author = "Xidias, E.K. and Nearchou, A.C. and Aspragathos, N.A.",
title = "Vehicle scheduling in 2D shop floor environments",
journal = "Industrial Robot",
year = 2009,
volume = 36,
number = 2,
pages = "176-183",
note = "cited By (since 1996)4",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-67849101781&partnerID=40&md5=eaf2e7d8cbc3f437dce9c8eda050c72e",
affiliation = "Department of Mechanical and Aeronautics Engineering, University of Patras, Patras, Greece; Department of Business Administration, University of Patras, Patras, Greece",
abstract = "Purpose - The purpose of this paper is to develop an efficient method for solving a vehicle scheduling problem (VSP) in 2D industrial environments. An autonomous vehicle is requested to serve a set of work centers in the shop floor providing transport and delivery tasks while avoiding collisions with obstacles during its travel. The objective is to find a minimum in length, collision-free vehicle routing schedule that serves timely as many as possible work centers in the shop floor. Design/methodology/approach - First, the vehicle's environment is mapped into a 2D B-Spline surface embedded in 3D Euclidean space using a robust geometric model. Then, a modified genetic algorithm is applied on the generated surface to search for an optimum legal route schedule that satisfies the requirements of the vehicle's mission. Findings - Simulation experiments show that the method is robust enough and can determine in a reasonable computation time a solution to VSP under consideration. Originality/value - There is a gap in the literature for methods that face VSP in shop-floor environments. This paper contributes to filling this gap by implementing a practical method that can be easily programmed and included in a modern service delivery system."
}

P Zacharia, I G Mariolis, N Aspragathos and E S Dermatas. Robot-handling fabrics with curved edges based on visual servoing and polygonal approximation. Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture 222(10):1263-1274, 2008. URL, AbstractThe main scope of this work is the development of a robot controller for the manipulation of fabrics lying on a work table towards the sewing process. A fuzzy visual servoing manipulator controller is developed to guide the fabric along the sewing line. The paper focuses on handling fabrics with curved edges by locally approximating the curve section with straight-line segments. An innovative algorithm based on the dominant point detection method and the genetic-based method is incorporated in the robot visual servoing system to achieve sewing of the curved edges. Simulation and experimental tests are conducted to evaluate the performance of the proposed algorithm. The results demonstrate that this approach is efficient and effective for the polygonal approximation, and the proposed robotic system is proved to be robust and efficient, achieving acceptable seam accuracy in the minimum time.BibTeX

@article{Zacharia01102008,
author = "Zacharia, P and Mariolis, I G and Aspragathos, N and Dermatas, E S",
title = "Robot-handling fabrics with curved edges based on visual servoing and polygonal approximation",
volume = 222,
number = 10,
pages = "1263-1274",
year = 2008,
doi = "10.1243/09544054JEM999",
abstract = "The main scope of this work is the development of a robot controller for the manipulation of fabrics lying on a work table towards the sewing process. A fuzzy visual servoing manipulator controller is developed to guide the fabric along the sewing line. The paper focuses on handling fabrics with curved edges by locally approximating the curve section with straight-line segments. An innovative algorithm based on the dominant point detection method and the genetic-based method is incorporated in the robot visual servoing system to achieve sewing of the curved edges. Simulation and experimental tests are conducted to evaluate the performance of the proposed algorithm. The results demonstrate that this approach is efficient and effective for the polygonal approximation, and the proposed robotic system is proved to be robust and efficient, achieving acceptable seam accuracy in the minimum time.",
url = "http://pib.sagepub.com/content/222/10/1263.abstract",
eprint = "http://pib.sagepub.com/content/222/10/1263.full.pdf+html",
journal = "Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture"
}

E K Xidias, P N Azariadis and N A Aspragathos. Path planning of holonomic and non-holonomic robots using bump-surfaces. Computer-Aided Design and Applications 5(1-4):497-507, 2008. URL, AbstractThis paper presents a global solution to a general problem of planning an optimum path of a robot moving in two dimensional environments. The proposed method is able to deal with both holonomic and non-holonomic robots moving into dynamic 2D environments with static and/or moving obstacles. The proposed method is based on the Bump-Surfaces concept which is used to represent the entire robot's environment. The introduced method is general and easy to implement and can be applied virtually to any dimensional or point robot. The performance of the proposed method is investigated and discussed through selected simulated experiments.BibTeX

@article{Xidias2008497,
author = "Xidias, E.K. and Azariadis, P.N. and Aspragathos, N.A.",
title = "Path planning of holonomic and non-holonomic robots using bump-surfaces",
journal = "Computer-Aided Design and Applications",
year = 2008,
volume = 5,
number = "1-4",
pages = "497-507",
note = "cited By (since 1996)2",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-70449531129&partnerID=40&md5=69785c7480e7f7c9e333666ae27e25b1",
affiliation = "University of Patras, Greece; University of the Aegean, Greece",
abstract = "This paper presents a global solution to a general problem of planning an optimum path of a robot moving in two dimensional environments. The proposed method is able to deal with both holonomic and non-holonomic robots moving into dynamic 2D environments with static and/or moving obstacles. The proposed method is based on the Bump-Surfaces concept which is used to represent the entire robot's environment. The introduced method is general and easy to implement and can be applied virtually to any dimensional or point robot. The performance of the proposed method is investigated and discussed through selected simulated experiments."
}

E K Xidias and N A Aspragathos. Motion planning for multiple non-holonomic robots: A geometric approach. Robotica 26(4):525-536, 2008. URL, AbstractIn this paper, a geometrical approach is developed to generate simultaneously optimal (or near-optimal) smooth paths for a set of non-holonomic robots, moving only forward in a 2D environment cluttered with static and moving obstacles. The robots environment is represented by a 3D geometric entity called Bump-Surface, which is embedded in a 4D Euclidean space. The multi-motion planning problem (MMPP) is resolved by simultaneously finding the paths for the set of robots represented by monoparametric smooth C2 curves onto the Bump-Surface, such that their inverse images onto the initial 2D workspace satisfy the optimization motion-planning criteria and constraints. The MMPP is expressed as an optimization problem, which is solved on the Bump-Surface using a genetic algorithm. The performance of the proposed approach is tested through a considerable number of simulated 2D dynamic environments with car-like robots.BibTeX

@article{Xidias2008525,
author = "Xidias, E.K. and Aspragathos, N.A.",
title = "Motion planning for multiple non-holonomic robots: A geometric approach",
journal = "Robotica",
year = 2008,
volume = 26,
number = 4,
pages = "525-536",
note = "cited By (since 1996)3",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-47949117941&partnerID=40&md5=6943335cfbb768d04bad21d8eda410b7",
affiliation = "Department of Mechanical and Aeronautics Engineering, University of Patras, Patras, 26500, Greece",
abstract = "In this paper, a geometrical approach is developed to generate simultaneously optimal (or near-optimal) smooth paths for a set of non-holonomic robots, moving only forward in a 2D environment cluttered with static and moving obstacles. The robots environment is represented by a 3D geometric entity called Bump-Surface, which is embedded in a 4D Euclidean space. The multi-motion planning problem (MMPP) is resolved by simultaneously finding the paths for the set of robots represented by monoparametric smooth C2 curves onto the Bump-Surface, such that their inverse images onto the initial 2D workspace satisfy the optimization motion-planning criteria and constraints. The MMPP is expressed as an optimization problem, which is solved on the Bump-Surface using a genetic algorithm. The performance of the proposed approach is tested through a considerable number of simulated 2D dynamic environments with car-like robots."
}

G T Zoumponos and N A Aspragathos. Fuzzy logic path planning for the robotic placement of fabrics on a work table. Robotics and Computer-Integrated Manufacturing 24(2):174-186, 2008. URL, AbstractIn this paper, an innovative fuzzy logic approach for the robotic laying of fabrics on a work table and based on fuzzy sets is presented. Through handling experiments the solution domain for the path of the robotic gripper is determined, the handling parameters are identified and implicit knowledge is accumulated. Then a proper scheme for the data acquisition is formed and a path-planning algorithm based on fuzzy logic is developed. Due to conflicts and inaccuracies of the acquired data, a subtractive clustering algorithm is used, to identify the proper clusters for the two developed fuzzy systems, with the first employing the clusters as rules and the second a neuro-fuzzy system initialised by the implicit knowledge and trained via back-propagation. Finally, the effectiveness of the two path-planning systems is investigated in an experimental stage where the robot successfully places on a table fabrics of a variety of materials and sizes.BibTeX

@article{Zoumponos2008174,
author = "Zoumponos, G.T. and Aspragathos, N.A.",
title = "Fuzzy logic path planning for the robotic placement of fabrics on a work table",
journal = "Robotics and Computer-Integrated Manufacturing",
year = 2008,
volume = 24,
number = 2,
pages = "174-186",
note = "cited By (since 1996)13",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-36148993518&partnerID=40&md5=bfae943fe2b816378cbc1834813b0383",
affiliation = "Mechanical and Aeronautics Engineering Department, University of Patras, 26500 Patra, Greece",
abstract = "In this paper, an innovative fuzzy logic approach for the robotic laying of fabrics on a work table and based on fuzzy sets is presented. Through handling experiments the solution domain for the path of the robotic gripper is determined, the handling parameters are identified and implicit knowledge is accumulated. Then a proper scheme for the data acquisition is formed and a path-planning algorithm based on fuzzy logic is developed. Due to conflicts and inaccuracies of the acquired data, a subtractive clustering algorithm is used, to identify the proper clusters for the two developed fuzzy systems, with the first employing the clusters as rules and the second a neuro-fuzzy system initialised by the implicit knowledge and trained via back-propagation. Finally, the effectiveness of the two path-planning systems is investigated in an experimental stage where the robot successfully places on a table fabrics of a variety of materials and sizes."
}

S Mekid, T Schlegel, N Aspragathos and R Teti. Foresight formulation in innovative production, automation and control systems. Foresight 9(5):35-47, 2007. URL, AbstractPurpose - This paper aims to define imminent and future key aspects in innovative production machines and systems but more specifically to focus on the automation and control aspects. Design/methodology/approach - The foresight analysis is based on the state-of-the-art of current manufacturing technologies with a setup of key enabling features and a roadmap research. Findings - The paper finds that more integration of current and future technology development is required to build a strong platform for various applications featured with interoperability, trust, security and protection. Autonomy and close collaboration aspects in machines remain as crucial targets for the near future. An immediate action is required on smart strategies for the design patterns and agents to enable intuitive components for high quality dynamic user interfaces. This will allow rapid configuration and adaptation to new manufacturing tasks with highly improved machine learning. Originality/value - The paper describes the future of key aspects required to move the production, automation and control systems forward.BibTeX

@article{Mekid200735,
author = "Mekid, S. and Schlegel, T. and Aspragathos, N. and Teti, R.",
title = "Foresight formulation in innovative production, automation and control systems",
journal = "Foresight",
year = 2007,
volume = 9,
number = 5,
pages = "35-47",
note = "cited By (since 1996)6",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-34548537957&partnerID=40&md5=31f943169d9468e42a7af32c625b4e5a",
affiliation = "University of Manchester, Manchester, United Kingdom; Fraunhofer Institute, IAO, Stuttgart, Germany; University of Patras, Patras, Greece; University of Naples Federico II, Naples, Italy",
abstract = "Purpose - This paper aims to define imminent and future key aspects in innovative production machines and systems but more specifically to focus on the automation and control aspects. Design/methodology/approach - The foresight analysis is based on the state-of-the-art of current manufacturing technologies with a setup of key enabling features and a roadmap research. Findings - The paper finds that more integration of current and future technology development is required to build a strong platform for various applications featured with interoperability, trust, security and protection. Autonomy and close collaboration aspects in machines remain as crucial targets for the near future. An immediate action is required on smart strategies for the design patterns and agents to enable intuitive components for high quality dynamic user interfaces. This will allow rapid configuration and adaptation to new manufacturing tasks with highly improved machine learning. Originality/value - The paper describes the future of key aspects required to move the production, automation and control systems forward."
}

E K Xidias, P N Azariadis and N A Aspragathos. Two-dimensional motion-planning for nonholonomic robots using the bump-surfaces concept. Computing (Vienna/New York) 79(2-4):109-118, 2007. URL, AbstractIn this paper, a new method is introduced for finding a near-optimal path of a nonholonomic robot moving in a 2D environment cluttered with static obstacles. The method is based on the Bump-Surfaces concept and is able to deal with robots represented by a translating and rotating rigid body. The proposed approach is applied to car-like robots.BibTeX

@article{Xidias2007109,
author = "Xidias, E.K. and Azariadis, P.N. and Aspragathos, N.A.",
title = "Two-dimensional motion-planning for nonholonomic robots using the bump-surfaces concept",
journal = "Computing (Vienna/New York)",
year = 2007,
volume = 79,
number = "2-4",
pages = "109-118",
note = "cited By (since 1996)5",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-34147142484&partnerID=40&md5=f5c906a40bc015a903f350ffb3c1c713",
affiliation = "Department of Mechanical and Aeronautics Engineering, University of Patras, Patras, 26500, Greece; Department of Product and Systems Design Engineering, University of the Aegean, Ermoupolis, Syros, 84100, Greece",
abstract = "In this paper, a new method is introduced for finding a near-optimal path of a nonholonomic robot moving in a 2D environment cluttered with static obstacles. The method is based on the Bump-Surfaces concept and is able to deal with robots represented by a translating and rotating rigid body. The proposed approach is applied to car-like robots."
}

P N Koustoumpardis, J S Fourkiotis and N A Aspragathos. Intelligent evaluation of fabrics' extensibility from robotized tensile test. International Journal of Clothing Science and Technology 19(2):80-98, 2007. URL, AbstractPurpose - The paper aims to propose an approach to intelligent evaluation of the tensile test. A robotized system is used that performs the fabrics tensile test and estimates the extensibility of the samples using a feed-forward neural network while trying to imitate the human expert estimation. Design/methodology/approach - The specifications of the tensile test are derived by an extensive observation of the respective experts' estimation performance. The fabric sample size and the experimental conditions are specified. Linguistic values of the term "fabric extensibility" are extracted through a knowledge acquisition process. The tensile test is performed by a robot manipulator with a simple gripper and the experimental measurements (force, strain) are fed online into a neural network. The network is trained according to the extensibility estimations of the experts. The trained network is tested in estimating unknown fabric's extensibility. Findings - The results demonstrate that the system is capable of estimating the extensibility of new fabrics. Originality/value - This work can be integrated in the robotized sewing process with intelligent control where the fabric's extensibility in terms of linguistic values is necessary. The proposed system initiates a new approach, in which the fabric properties are expressed and used in a way that will facilitate the introduction of the artificial intelligence methods into the clothing industry.BibTeX

@article{Koustoumpardis200780,
author = "Koustoumpardis, P.N. and Fourkiotis, J.S. and Aspragathos, N.A.",
title = "Intelligent evaluation of fabrics' extensibility from robotized tensile test",
journal = "International Journal of Clothing Science and Technology",
year = 2007,
volume = 19,
number = 2,
pages = "80-98",
note = "cited By (since 1996)4",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-33847110219&partnerID=40&md5=7e45899487d8d6ef7e58a7fdce524368",
affiliation = "Department of Mechanical and Aeronautics Engineering, University of Patras, Patras, Greece",
abstract = {Purpose - The paper aims to propose an approach to intelligent evaluation of the tensile test. A robotized system is used that performs the fabrics tensile test and estimates the extensibility of the samples using a feed-forward neural network while trying to imitate the human expert estimation. Design/methodology/approach - The specifications of the tensile test are derived by an extensive observation of the respective experts' estimation performance. The fabric sample size and the experimental conditions are specified. Linguistic values of the term "fabric extensibility" are extracted through a knowledge acquisition process. The tensile test is performed by a robot manipulator with a simple gripper and the experimental measurements (force, strain) are fed online into a neural network. The network is trained according to the extensibility estimations of the experts. The trained network is tested in estimating unknown fabric's extensibility. Findings - The results demonstrate that the system is capable of estimating the extensibility of new fabrics. Originality/value - This work can be integrated in the robotized sewing process with intelligent control where the fabric's extensibility in terms of linguistic values is necessary. The proposed system initiates a new approach, in which the fabric properties are expressed and used in a way that will facilitate the introduction of the artificial intelligence methods into the clothing industry.}
}

E K Xidias, P N Azariadis and N A Aspragathos. Energy-minimizing motion design for nonholonomic robots amidst moving obstacles. Computer-Aided Design and Applications 3(1-4):165-174, 2006. URL, AbstractIn this paper, a new method is introduced for computing energy-minimizing motions in two-dimensional environments cluttered with a priori known static and moving obstacles. The proposed method is based on a new four-dimensional motion-planning space represented by a Bump-Surface embedded in β„›. The energy-minimizing motion-design problem is expressed by a variational curve-design problem on the introduced Bump-Surface. The optimal motion is determined by a new algorithm for computing a B-spline curve on the Bump-Surface which is conformal to the motion-planning constrains. The proposed method is applied for designing the motion of nonholonomic robots in the presence of moving obstacles and its performance is tested in simulated 2D dynamic environments with car-like robots.BibTeX

@article{Xidias2006165,
author = "Xidias, E.K. and Azariadis, P.N. and Aspragathos, N.A.",
title = "Energy-minimizing motion design for nonholonomic robots amidst moving obstacles",
journal = "Computer-Aided Design and Applications",
year = 2006,
volume = 3,
number = "1-4",
pages = "165-174",
note = "cited By (since 1996)2",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-33744827733&partnerID=40&md5=b1c8c3a6a65c4dde16a9f0240d133385",
affiliation = "University of Patras, Greece; University of the Aegean, Greece",
abstract = "In this paper, a new method is introduced for computing energy-minimizing motions in two-dimensional environments cluttered with a priori known static and moving obstacles. The proposed method is based on a new four-dimensional motion-planning space represented by a Bump-Surface embedded in β„›. The energy-minimizing motion-design problem is expressed by a variational curve-design problem on the introduced Bump-Surface. The optimal motion is determined by a new algorithm for computing a B-spline curve on the Bump-Surface which is conformal to the motion-planning constrains. The proposed method is applied for designing the motion of nonholonomic robots in the presence of moving obstacles and its performance is tested in simulated 2D dynamic environments with car-like robots."
}

S G Papageorgiou and N A Aspragathos. Transformation and normal vector calculation of parametrically defined surfaces based on dual vectors and screw theory: Application to Phong's shading model. Computer Graphics Forum 25(2):183-195, 2006. URL, AbstractThis paper presents a new approach for the transformation and normal vector calculation algorithms of parametrically defined surfaces via dual vectors and line transformations. The surface is defined via dual points, the transformation is performed by rotations and translations based on screw theory while normal vector calculation is utilized for shading based on Phong's illumination model. The main benefit of this approach lies into the compactness of the surface's representation since geometrical characteristics, such as tangent vectors, that are necessary for shading algorithms, are included within its definition. An extensive comparison is performed between the proposed approach and the traditional homogeneous model, presenting the merits of our approach. Analytical and experimental determination of the computational cost via computer implementation of 3D surface transformation and shading is presented. Point-based methods for the representation, transformation and shading of parametrically defined surfaces are compared to the introduced line-based methods (dual quaternions and dual orthogonal matrices). It is shown that the simplified rendering procedure of 3D objects, is considerably faster using screw theory over the traditional point-based structures.BibTeX

@article{Papageorgiou2006183,
author = "Papageorgiou, S.G. and Aspragathos, N.A.",
title = "Transformation and normal vector calculation of parametrically defined surfaces based on dual vectors and screw theory: Application to Phong's shading model",
journal = "Computer Graphics Forum",
year = 2006,
volume = 25,
number = 2,
pages = "183-195",
note = "cited By (since 1996)1",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-33745472169&partnerID=40&md5=a62141f6addaff82d39afd15610588d0",
affiliation = "Robotics Group, Department of Mechanical and Aeronautical Engineering, University of Patras, 26500 Patra, Greece",
abstract = "This paper presents a new approach for the transformation and normal vector calculation algorithms of parametrically defined surfaces via dual vectors and line transformations. The surface is defined via dual points, the transformation is performed by rotations and translations based on screw theory while normal vector calculation is utilized for shading based on Phong's illumination model. The main benefit of this approach lies into the compactness of the surface's representation since geometrical characteristics, such as tangent vectors, that are necessary for shading algorithms, are included within its definition. An extensive comparison is performed between the proposed approach and the traditional homogeneous model, presenting the merits of our approach. Analytical and experimental determination of the computational cost via computer implementation of 3D surface transformation and shading is presented. Point-based methods for the representation, transformation and shading of parametrically defined surfaces are compared to the introduced line-based methods (dual quaternions and dual orthogonal matrices). It is shown that the simplified rendering procedure of 3D objects, is considerably faster using screw theory over the traditional point-based structures."
}

T Velten, H H Ruf, D Barrow, N Aspragathos, P Lazarou, E Jung, C K Malek, M Richter, J Kruckow and M Wackerle. Packaging of bio-MEMS: Strategies, technologies, and applications. IEEE Transactions on Advanced Packaging 28(4):533-546, 2005. URL, AbstractBiomicroelectromechanical systems (bio-MEMS) are MEMS which are designed for medical or biological applications. As with other MEMS, bio-MEMS frequently, have to be packaged to provide an interface to the macroscale world of the user. Bio-MEMS can be toughly divided in two groups. Bio-MEMS can be pure technical systems applied in a biological environment or technical systems which integrate biological materials as one functional camponent of the system. In both cases, the materials which have intimate contact to biological matter have to be biocompatible to avoid unintentional effects on the biological substances, which in case of medical implants, could harm the patient. In the case of biosensors, the use of nonbiocompatible materials could interfere with the biological subcomponents which would affect the sensor's performance. Bio-MEMS containing biological subcomponents require the use of "biocompatible" technologies for assembly and packaging; e.g., high temperatures occurring, for instance, during thermosonic wire bonding and other thermobonding processes would denature the bioaffinity layers on biosensor chips. This means that the use of selected or alternative packaging and assembly methods, or new strategies, is necessary for a wide range of bio-MEMS applications. This paper provides an overview of some of the strategies, technologies, and applications in the field of bio-MEMS packaging. It includes the following: β€Ά strategies for the partitioning of subsystems within int egrated microsystems for (bio)chemical analysis/synthesis; β€Ά methods for micr oassembly of bio-MEMS; β€Ά technologies for bondin g of polymer bio-MEMS components; β€Ά packa ging of miniature medical devices; β€Ά packaging of biesensor s for in vitro applications; β€Ά packaging o f mikropumps as a bio-MEMS component. The applications discussed are derived from different fields to demonstrate the plethora of bio-MEMS considerations. In commercial production, packaging is possibly the major cost factor of bio-MEMS-based products, and its development requires special attention.BibTeX

@article{Velten2005533,
author = "Velten, T. and Ruf, H.H. and Barrow, D and Aspragathos, N. and Lazarou, P. and Jung, E. and Malek, C.K. and Richter, M. and Kruckow, J. and Wackerle, M.",
title = "Packaging of bio-MEMS: Strategies, technologies, and applications",
journal = "IEEE Transactions on Advanced Packaging",
year = 2005,
volume = 28,
number = 4,
pages = "533-546",
note = "cited By (since 1996)36",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-28444487187&partnerID=40&md5=dcda38b6ad951ec4b97b66cf91e228e9",
affiliation = "Fraunhofer Institute for Biomedical Engineering (IBMT), 66386 St. Ingbert, Germany; Cardiff School of Engineering, Cardiff University, Cardiff CF24 3TF, United Kingdom; Robotics Group Mechanical and Aeronautics Engineering Department, University of Patras, 26500 Rion, Greece; Fraunhofer Institute for Reliability and Microintegration (IZM), 13355 Berlin, Germany; Lab. Franche-Comte Electron. Mecanique Thermique Optique-Sciences et T echnologies, 25044 BesanΓ§on, France; Fraunhofer Institute for Reliability and MicrointegratΓ­on (IZM), 80686 Munich, Germany; Universit-dsat des Saarlandes, SaarbrΓΌken, Germany",
abstract = {Biomicroelectromechanical systems (bio-MEMS) are MEMS which are designed for medical or biological applications. As with other MEMS, bio-MEMS frequently, have to be packaged to provide an interface to the macroscale world of the user. Bio-MEMS can be toughly divided in two groups. Bio-MEMS can be pure technical systems applied in a biological environment or technical systems which integrate biological materials as one functional camponent of the system. In both cases, the materials which have intimate contact to biological matter have to be biocompatible to avoid unintentional effects on the biological substances, which in case of medical implants, could harm the patient. In the case of biosensors, the use of nonbiocompatible materials could interfere with the biological subcomponents which would affect the sensor's performance. Bio-MEMS containing biological subcomponents require the use of "biocompatible" technologies for assembly and packaging; e.g., high temperatures occurring, for instance, during thermosonic wire bonding and other thermobonding processes would denature the bioaffinity layers on biosensor chips. This means that the use of selected or alternative packaging and assembly methods, or new strategies, is necessary for a wide range of bio-MEMS applications. This paper provides an overview of some of the strategies, technologies, and applications in the field of bio-MEMS packaging. It includes the following: β€Ά strategies for the partitioning of subsystems within int egrated microsystems for (bio)chemical analysis/synthesis; β€Ά methods for micr oassembly of bio-MEMS; β€Ά technologies for bondin g of polymer bio-MEMS components; β€Ά packa ging of miniature medical devices; β€Ά packaging of biesensor s for in vitro applications; β€Ά packaging o f mikropumps as a bio-MEMS component. The applications discussed are derived from different fields to demonstrate the plethora of bio-MEMS considerations. In commercial production, packaging is possibly the major cost factor of bio-MEMS-based products, and its development requires special attention.}
}

P N Azariadis and N A Aspragathos. Obstacle representation by Bump-surfaces for optimal motion-planning. Robotics and Autonomous Systems 51(2-3):129-150, 2005. URL, AbstractThis paper introduces a new method for global, near optimal, motion-planning of a robot (either mobile or redundant manipulator) moving in an environment cluttered with a priori known prohibited areas which have arbitrary shape, size and location. The proposed method is based on the novel notion of Bump-surfaces (or B-surfaces) which represent the entire robot environment through a single mathematical entity. The motion-planning solution is searched on a higher-dimension B-surface in such a way that its inverse image into the robot environment satisfies the given objectives and constraints. The computed solution for a mobile robot consists of a smooth curve without self-loops which connects the starting and destination points with the shortest possible path. The same approach is also used for nth degree-of-freedom manipulators where the end-effector reaches the destination position following a smooth short path avoiding the prohibited areas. For clarity reasons the proposed method is introduced in this paper for the case of a two-dimensional (2D) planar terrain with static obstacles, while a generalization to motion-planning problems on curved terrains is also discussed. Extensive experiments are presented and discussed to illustrate the efficiency and effectiveness of the proposed motion-planning method in a variety of complex environments.BibTeX

@article{Azariadis2005129,
author = "Azariadis, P.N. and Aspragathos, N.A.",
title = "Obstacle representation by Bump-surfaces for optimal motion-planning",
journal = "Robotics and Autonomous Systems",
year = 2005,
volume = 51,
number = "2-3",
pages = "129-150",
note = "cited By (since 1996)17",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-16644365470&partnerID=40&md5=f15a649735857c0646476252a4b9a3bf",
affiliation = "University of the Aegean, Dept. of Prod. and Syst. Des. Eng., 84100 Ermoupolis, Syros, Greece; ELKEDE - Technol. and Des. Centre SA, Research and Technology Department, 14452 Metamorphosis, Greece; University of Patras, Mech. Eng. and Aero. Department, 26500 Patras, Greece",
abstract = "This paper introduces a new method for global, near optimal, motion-planning of a robot (either mobile or redundant manipulator) moving in an environment cluttered with a priori known prohibited areas which have arbitrary shape, size and location. The proposed method is based on the novel notion of Bump-surfaces (or B-surfaces) which represent the entire robot environment through a single mathematical entity. The motion-planning solution is searched on a higher-dimension B-surface in such a way that its inverse image into the robot environment satisfies the given objectives and constraints. The computed solution for a mobile robot consists of a smooth curve without self-loops which connects the starting and destination points with the shortest possible path. The same approach is also used for nth degree-of-freedom manipulators where the end-effector reaches the destination position following a smooth short path avoiding the prohibited areas. For clarity reasons the proposed method is introduced in this paper for the case of a two-dimensional (2D) planar terrain with static obstacles, while a generalization to motion-planning problems on curved terrains is also discussed. Extensive experiments are presented and discussed to illustrate the efficiency and effectiveness of the proposed motion-planning method in a variety of complex environments."
}

P.Th. Zacharia and N A Aspragathos. Optimal robot task scheduling based on genetic algorithms. Robotics and Computer-Integrated Manufacturing 21(1):67-79, 2005. URL, AbstractIndustrial robots should perform complex tasks in the minimum possible cycle time in order to obtain high productivity. The problem of determining the optimum route of a manipulator's end effector visiting a number of task points is similar but not identical to the well-known travelling salesman problem (TSP). Adapting TSP to Robotics, the measure to be optimized is the time instead of the distance. In addition, the travel time between any two points is significantly affected by the choice of the manipulator's configuration. Therefore, the multiple solutions of the inverse kinematics problem should be taken into consideration. In this paper, a method is introduced to determine the optimum sequence of task points visited by the tip of the end effector of an articulated robot and it can be applied to any non-redundant manipulator. This method is based on genetic algorithms and an innovative encoding is introduced to take into account the multiple solutions of the inverse kinematic problem. The results show that the method can determine the optimum sequence of a considerable number of task points for robots up to six-degrees of freedom.BibTeX

@article{Zacharia200567,
author = "Zacharia, P.Th. and Aspragathos, N.A.",
title = "Optimal robot task scheduling based on genetic algorithms",
journal = "Robotics and Computer-Integrated Manufacturing",
year = 2005,
volume = 21,
number = 1,
pages = "67-79",
note = "cited By (since 1996)39",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-7044222041&partnerID=40&md5=a3296080b19fd4d525d0815787bb931c",
affiliation = "Mechanical Engineering Department, University of Patras, 26500 Patras, Greece",
abstract = "Industrial robots should perform complex tasks in the minimum possible cycle time in order to obtain high productivity. The problem of determining the optimum route of a manipulator's end effector visiting a number of task points is similar but not identical to the well-known travelling salesman problem (TSP). Adapting TSP to Robotics, the measure to be optimized is the time instead of the distance. In addition, the travel time between any two points is significantly affected by the choice of the manipulator's configuration. Therefore, the multiple solutions of the inverse kinematics problem should be taken into consideration. In this paper, a method is introduced to determine the optimum sequence of task points visited by the tip of the end effector of an articulated robot and it can be applied to any non-redundant manipulator. This method is based on genetic algorithms and an innovative encoding is introduced to take into account the multiple solutions of the inverse kinematic problem. The results show that the method can determine the optimum sequence of a considerable number of task points for robots up to six-degrees of freedom."
}

V C Moulianitis, N A Aspragathos and A J Dentsoras. A model for concept evaluation in design - An application to mechatronics design of robot grippers. Mechatronics 14(6):599-622, 2004. URL, AbstractIn this paper, an approach for the modelling of the evaluation process in the conceptual design phase is presented. During the design process, the generated candidate solutions are evaluated. The evaluation is achieved by calculating a score that is based on specific criteria that are presented as elements of a vector. Weight factors are applied to highlight the importance of each criterion. The formulation of the evaluation score is based on t-norm and averaging operators with the assumption that the universe of discourse of criteria is. A discussion of the meaning of these operators and a comparative study of them is presented. As an application, the mechatronics design of robot grippers for handling fabrics is analysed. The elements of the mechatronics index are presented in terms of flexibility, intelligence and complexity. This index is formulated using the variety of the t-norms and averaging operators to show the weaks and strengths of each of them.BibTeX

@article{Moulianitis2004599,
author = "Moulianitis, V.C. and Aspragathos, N.A. and Dentsoras, A.J.",
title = "A model for concept evaluation in design - An application to mechatronics design of robot grippers",
journal = "Mechatronics",
year = 2004,
volume = 14,
number = 6,
pages = "599-622",
note = "cited By (since 1996)17",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-1842560229&partnerID=40&md5=045fd71001f409d144889605895ca064",
affiliation = "Mechanical Engineering Department, University of Patras, Patras 26500, Greece",
abstract = "In this paper, an approach for the modelling of the evaluation process in the conceptual design phase is presented. During the design process, the generated candidate solutions are evaluated. The evaluation is achieved by calculating a score that is based on specific criteria that are presented as elements of a vector. Weight factors are applied to highlight the importance of each criterion. The formulation of the evaluation score is based on t-norm and averaging operators with the assumption that the universe of discourse of criteria is. A discussion of the meaning of these operators and a comparative study of them is presented. As an application, the mechatronics design of robot grippers for handling fabrics is analysed. The elements of the mechatronics index are presented in terms of flexibility, intelligence and complexity. This index is formulated using the variety of the t-norms and averaging operators to show the weaks and strengths of each of them."
}

P N Koustoumpardis and N A Aspragathos. Fuzzy logic decision mechanism combined with a neuro-controller for fabric tension in robotized sewing process. Journal of Intelligent and Robotic Systems: Theory and Applications 36(1):65-88, 2003. URL, AbstractA new approach for flexible automated handling of fabrics in the sewing process is described, which focuses to control the cloth tension applied by a robot. The proposed hierarchical robot control system includes a Fuzzy decision mechanism combined with a Neuro-controller. The expert's actions during the sewing process are investigated and this human behavior is interpreted in order to design the controller. The Fuzzy Logic decision mechanism utilizes only qualitative knowledge concerning the properties of the fabrics, in order to determine the desired tensional force and the location of the robot hand on the fabric. A Neural Network controller regulates the fabric tension to achieve the desired value by determining the robot end effector velocity. The simulation results demonstrate the efficiency of the system as well as the robustness of the controller performance since the effects of the noise are negligible. The system capabilities are more evident when the controller uses its previously acquired "experience".BibTeX

@article{Koustoumpardis200365,
author = "Koustoumpardis, P.N. and Aspragathos, N.A.",
title = "Fuzzy logic decision mechanism combined with a neuro-controller for fabric tension in robotized sewing process",
journal = "Journal of Intelligent and Robotic Systems: Theory and Applications",
year = 2003,
volume = 36,
number = 1,
pages = "65-88",
note = "cited By (since 1996)9",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0037234718&partnerID=40&md5=ec7d629c20f88d660a0f0f69f5a81124",
affiliation = "Department of Mechanical Engineering, University of Patras, 26110 Patras, Greece",
abstract = {A new approach for flexible automated handling of fabrics in the sewing process is described, which focuses to control the cloth tension applied by a robot. The proposed hierarchical robot control system includes a Fuzzy decision mechanism combined with a Neuro-controller. The expert's actions during the sewing process are investigated and this human behavior is interpreted in order to design the controller. The Fuzzy Logic decision mechanism utilizes only qualitative knowledge concerning the properties of the fabrics, in order to determine the desired tensional force and the location of the robot hand on the fabric. A Neural Network controller regulates the fabric tension to achieve the desired value by determining the robot end effector velocity. The simulation results demonstrate the efficiency of the system as well as the robustness of the controller performance since the effects of the noise are negligible. The system capabilities are more evident when the controller uses its previously acquired "experience".}
}

P N Azariadis, A C Nearchou and N A Aspragathos. An evolutionary algorithm for generating planar developments of arbitrarily curved surfaces. Computers in Industry 47(3):357-368, 2002. URL, AbstractIn this paper, a new method based on constrained global optimization is proposed for generating planar developments of arbitrarily three-dimensional surfaces. With this method an initial planar development is derived which is refined in order to satisfy certain criteria. This refinement is formulated as a global minimization problem under constraints. Generally, the constraints are used to control the local accuracy in the derived planar development. The overall minimization problem is resolved using a real-coded genetic algorithms (GA), which is developed for resolving multi-dimensional minimization problems. Indicative applications are presented to illustrate the effectiveness of the proposed method.BibTeX

@article{Azariadis2002357,
author = "Azariadis, P.N. and Nearchou, A.C. and Aspragathos, N.A.",
title = "An evolutionary algorithm for generating planar developments of arbitrarily curved surfaces",
journal = "Computers in Industry",
year = 2002,
volume = 47,
number = 3,
pages = "357-368",
note = "cited By (since 1996)11",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0036495879&partnerID=40&md5=27ac75484637f60cf9b23629b8c24bda",
affiliation = "Mechanical Engineering and Aeronautics Department, University of Patras, 26 500 Patras, Greece; Business Administration Department, University of Patras, 26 500 Patras, Greece",
abstract = "In this paper, a new method based on constrained global optimization is proposed for generating planar developments of arbitrarily three-dimensional surfaces. With this method an initial planar development is derived which is refined in order to satisfy certain criteria. This refinement is formulated as a global minimization problem under constraints. Generally, the constraints are used to control the local accuracy in the derived planar development. The overall minimization problem is resolved using a real-coded genetic algorithms (GA), which is developed for resolving multi-dimensional minimization problems. Indicative applications are presented to illustrate the effectiveness of the proposed method."
}

N A Aspragathos and S Foussias. Optimal location of a robot path when considering velocity performance. Robotica 20(2):139-147, 2002. URL, AbstractA method for searching the best location of a path in the robot workspace considering the velocity performance of the robot is presented. After a thorough investigation of the robot performance indices, a new measure for the velocity efficiency of a robot moving its end-effector along a path is introduced. This measure is an approximation of the minimum of the Manipulator Velocity Ratio (MVR) along the path. The minimum is calculated from a finite set of MVRs determined at specified points of the path using an algorithm for an approximate motion of the end effector along the path. The introduced measure is used as the objective function in an optimisation problem, where an optimal location of the path is searched. The objective function is procedural and non continuous, so a Genetic Algorithm is used to search the space for the optimal location of the path. The proposed method is tested using a simulated PUMA-like robot, which has to move its end-effector along a straight-line segment. At the end of the paper, the results obtained in these tests are presented and discussed.BibTeX

@article{Aspragathos2002139,
author = "Aspragathos, N.A. and Foussias, S.",
title = "Optimal location of a robot path when considering velocity performance",
journal = "Robotica",
year = 2002,
volume = 20,
number = 2,
pages = "139-147",
note = "cited By (since 1996)13",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0036504897&partnerID=40&md5=7fe11156215dfcd4ee8605ac8f32b3d3",
affiliation = "Mechanical and Aero. Eng. Department, University of Patras, Patras, Greece",
abstract = "A method for searching the best location of a path in the robot workspace considering the velocity performance of the robot is presented. After a thorough investigation of the robot performance indices, a new measure for the velocity efficiency of a robot moving its end-effector along a path is introduced. This measure is an approximation of the minimum of the Manipulator Velocity Ratio (MVR) along the path. The minimum is calculated from a finite set of MVRs determined at specified points of the path using an algorithm for an approximate motion of the end effector along the path. The introduced measure is used as the objective function in an optimisation problem, where an optimal location of the path is searched. The objective function is procedural and non continuous, so a Genetic Algorithm is used to search the space for the optimal location of the path. The proposed method is tested using a simulated PUMA-like robot, which has to move its end-effector along a straight-line segment. At the end of the paper, the results obtained in these tests are presented and discussed."
}

N I Glossas and N A Aspragathos. Grasp and rotate fragile objects using fuzzy control and tactile sensor. Systems Science 27(4):23-34, 2001. URL, AbstractLast years a lot of research work has been devoted in the area of prosthetic hands towards achieving behaviour similar to that human hand. These prosthetic hand allow complicated operations such as grasping and manipulating of fragile objects to be realised. For the implementation of such prostheses, the patient receives signals coming from the environment, in order to allow an approximation of the sense of touch. In addition, sophisticated control systems, electronics and actuation have to be proposed, in order to obtain a better performance of the prosthetic hand. In this work, a new controller for artificial hands with two fingers used to grasp and rotate fragile and delicate objects is proposed. In this controller tactile feedback is used and the closing velocity of the fingers is adjusted, in order to grasp the object by applying the minimal required force and without the measurement of this force. The operation of the proposed controller is based on fuzzy logic for the following two reasons. The first is the ambition to achieve prosthetic hand behaviour similar to that of a human hand when it holds an object. The second reason is that using fuzzy logic the indispensable mathematics can be simplified in order to design a system operating in real time. Finally, the results from the comparison of the proposed controller efficiency with PID's are presented.BibTeX

@article{Glossas200123,
author = "Glossas, N.I. and Aspragathos, N.A.",
title = "Grasp and rotate fragile objects using fuzzy control and tactile sensor",
journal = "Systems Science",
year = 2001,
volume = 27,
number = 4,
pages = "23-34",
note = "cited By (since 1996)0",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0035788592&partnerID=40&md5=b38e495a4cfcf898dc1f3b72de27abbe",
affiliation = "Mech. Eng. and Aeronautics Dept., University of Patras, 26500 Patras, Greece",
abstract = "Last years a lot of research work has been devoted in the area of prosthetic hands towards achieving behaviour similar to that human hand. These prosthetic hand allow complicated operations such as grasping and manipulating of fragile objects to be realised. For the implementation of such prostheses, the patient receives signals coming from the environment, in order to allow an approximation of the sense of touch. In addition, sophisticated control systems, electronics and actuation have to be proposed, in order to obtain a better performance of the prosthetic hand. In this work, a new controller for artificial hands with two fingers used to grasp and rotate fragile and delicate objects is proposed. In this controller tactile feedback is used and the closing velocity of the fingers is adjusted, in order to grasp the object by applying the minimal required force and without the measurement of this force. The operation of the proposed controller is based on fuzzy logic for the following two reasons. The first is the ambition to achieve prosthetic hand behaviour similar to that of a human hand when it holds an object. The second reason is that using fuzzy logic the indispensable mathematics can be simplified in order to design a system operating in real time. Finally, the results from the comparison of the proposed controller efficiency with PID's are presented."
}

N I Glossas and N A Aspragathos. Fuzzy logic grasp control using tactile sensors. Mechatronics 11(7):899-920, 2001. URL, AbstractThis paper presents a method to control a two-fingers gripper for safe grasping of fragile and delicate objects like glass, fruits or vegetables. The proposed control algorithm adjusts the motion of the fingers of a gripper using tactile feedback, so that an object is grasped with the minimal required force without the measurement of this force. The rules set of the control law is derived empirically by investigation of the human finger skills. The formulation of these rules and the inference mechanism are based on fuzzy logic. The controller receives the object velocity and acceleration and the detection of incipient slippage and adjusts the fingers motion. The main advantage of this method is that the designed controller is quite robust because knowledge concerning the size, the weight or the surface texture of the grasped object is not required. The object is stably grasped by applying a relatively low grasping force. Simulated experiments are presented to demonstrate the efficiency of the introduced fuzzy controller of robot grippers, while its performance is compared with a PID controller.BibTeX

@article{Glossas2001899,
author = "Glossas, N.I and Aspragathos, N.A",
title = "Fuzzy logic grasp control using tactile sensors",
journal = "Mechatronics",
year = 2001,
volume = 11,
number = 7,
pages = "899-920",
note = "cited By (since 1996)32",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0035480195&partnerID=40&md5=3df9377c20fd01321f2dd6b4eaa45ad2",
affiliation = "Mechanical Engineering and Aeronautics Department, University of Patras, 26500 Patras, Greece",
abstract = "This paper presents a method to control a two-fingers gripper for safe grasping of fragile and delicate objects like glass, fruits or vegetables. The proposed control algorithm adjusts the motion of the fingers of a gripper using tactile feedback, so that an object is grasped with the minimal required force without the measurement of this force. The rules set of the control law is derived empirically by investigation of the human finger skills. The formulation of these rules and the inference mechanism are based on fuzzy logic. The controller receives the object velocity and acceleration and the detection of incipient slippage and adjusts the fingers motion. The main advantage of this method is that the designed controller is quite robust because knowledge concerning the size, the weight or the surface texture of the grasped object is not required. The object is stably grasped by applying a relatively low grasping force. Simulated experiments are presented to demonstrate the efficiency of the introduced fuzzy controller of robot grippers, while its performance is compared with a PID controller."
}

C J Tsaprounis and N A Aspragathos. A linear differential formulation of friction forces for adaptive estimator algorithms. Robotica 19(4):407-421, 2001. URL, AbstractIn this paper a new approach for the formulation of the friction forces velocity function is introduced. The scope of this formulation is to facilitate the implementation of control laws for systems where friction forces appear. The friction model includes the exponential decay part, the Coulomb and viscous friction. The introduced formulation is based on the observation that the friction coefficient function of velocity can be presented as the solution of a linear differential equation. Due to this linearity, the parameters of the derived differential equation can be estimated easily by an adaptive system. The estimation of these parameters is equivalent to the estimation of the friction coefficient in the full range of operational velocities. This knowledge gives to the designed control systems the potential to avoid successfully the stick-slip phenomenon. A control law for one D.O.F. system, where friction appears, is designed in order to prove the applicability of the proposed formulation of the friction model in control systems. A MRAC adaptive algorithm estimates the differential friction model parameters, using the measured friction force, while a sliding controller adjusts the motion of the mechanical system. The proposed friction model can be used in any control system where friction forces have to be compensated. The linear form of the model is suitable for common adaptive estimators. Therefore, the proposed structure is suitable for robotic applications, such as assembly, deburring, etc.BibTeX

@article{Tsaprounis2001407,
author = "Tsaprounis, C.J. and Aspragathos, N.A.",
title = "A linear differential formulation of friction forces for adaptive estimator algorithms",
journal = "Robotica",
year = 2001,
volume = 19,
number = 4,
pages = "407-421",
note = "cited By (since 1996)3",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0035387195&partnerID=40&md5=8b8ffcad7bbb0692b28a65c8fb6a6ce1",
affiliation = "University of Patras, Dept. of Mech. and Aeronautical Eng., Patras 26500, Greece",
abstract = "In this paper a new approach for the formulation of the friction forces velocity function is introduced. The scope of this formulation is to facilitate the implementation of control laws for systems where friction forces appear. The friction model includes the exponential decay part, the Coulomb and viscous friction. The introduced formulation is based on the observation that the friction coefficient function of velocity can be presented as the solution of a linear differential equation. Due to this linearity, the parameters of the derived differential equation can be estimated easily by an adaptive system. The estimation of these parameters is equivalent to the estimation of the friction coefficient in the full range of operational velocities. This knowledge gives to the designed control systems the potential to avoid successfully the stick-slip phenomenon. A control law for one D.O.F. system, where friction appears, is designed in order to prove the applicability of the proposed formulation of the friction model in control systems. A MRAC adaptive algorithm estimates the differential friction model parameters, using the measured friction force, while a sliding controller adjusts the motion of the mechanical system. The proposed friction model can be used in any control system where friction forces have to be compensated. The linear form of the model is suitable for common adaptive estimators. Therefore, the proposed structure is suitable for robotic applications, such as assembly, deburring, etc."
}

P N Azariadis and N A Aspragathos. Geodesic curvature preservation in surface flattening through constrained global optimization. CAD Computer Aided Design 33(8):581-591, 2001. URL, AbstractIn this paper, two methods for generating a planar development of a three-dimensional (3D) surface are proposed. The first method is based on the solution of a global optimization problem without constraints taking into consideration the geodesic curvature of the surface isoparametric curves. The second method is based on the solution of a global optimization problem subject to constraints which are used to control the local accuracy in the derived planar development. Contrarily to previous approaches the proposed second method does not depend on the surface parameterization, since the formed energy function and the proposed constraints are based only on the triangulation of the object surface. Several experiments illustrate that when the 3D surface is approximated with satisfying accuracy, modifications in the triangulation do not have any significant influence to the result of the proposed method. The proposed second method can be used without any modifications with trimmed surfaces, while the generated planar developments can also be used for minimally distorted texture mapping. Finally, the effectiveness of the proposed second method is illustrated through an indicative application in shoe designing.BibTeX

@article{Azariadis2001581,
author = "Azariadis, P.N. and Aspragathos, N.A.",
title = "Geodesic curvature preservation in surface flattening through constrained global optimization",
journal = "CAD Computer Aided Design",
year = 2001,
volume = 33,
number = 8,
pages = "581-591",
note = "cited By (since 1996)32",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0035398626&partnerID=40&md5=a15ed02e56cf3a7841c0110dd1414c15",
affiliation = "University of Patras, Department of Mechanical and Aeronautical Engineering, Laboratory of Machine Design, 26500 Patras, Greece",
abstract = "In this paper, two methods for generating a planar development of a three-dimensional (3D) surface are proposed. The first method is based on the solution of a global optimization problem without constraints taking into consideration the geodesic curvature of the surface isoparametric curves. The second method is based on the solution of a global optimization problem subject to constraints which are used to control the local accuracy in the derived planar development. Contrarily to previous approaches the proposed second method does not depend on the surface parameterization, since the formed energy function and the proposed constraints are based only on the triangulation of the object surface. Several experiments illustrate that when the 3D surface is approximated with satisfying accuracy, modifications in the triangulation do not have any significant influence to the result of the proposed method. The proposed second method can be used without any modifications with trimmed surfaces, while the generated planar developments can also be used for minimally distorted texture mapping. Finally, the effectiveness of the proposed second method is illustrated through an indicative application in shoe designing."
}

P Azariadis and N Aspragathos. Computer graphics representation and transformation of geometric entities using dual unit vectors and line transformations. Computers and Graphics (Pergamon) 25(2):195-209, 2001. URL, AbstractIn this paper, a representational model is proposed for the description and transformation of three-dimensional geometric entities in computer graphics. The structure of the proposed representation is based on dual unit vectors, while the corresponding transformations are carried out through dual unit quaternions or dual orthogonal matrices. The main advantage of this representation is its compactness since the additional useful geometric characteristics of a represented curve or surface such as a tangent or normal vector are incorporated within the actual representational structure itself. Rotations, translations and view transformations are naturally expressed using the concept of screw displacement, while scaling is accomplished utilizing the moment vector of each dual line. Furthermore, an analysis of the transform operator based on dual unit quaternions is presented in order to ascertain an efficient formula to be used in the implementation of a computational algorithm for computer animation. Finally, an analytical comparison between the proposed representational model and the usual homogeneous model in computer animation is presented showing the merits of our method.BibTeX

@article{Azariadis2001195,
author = "Azariadis, P. and Aspragathos, N.",
title = "Computer graphics representation and transformation of geometric entities using dual unit vectors and line transformations",
journal = "Computers and Graphics (Pergamon)",
year = 2001,
volume = 25,
number = 2,
pages = "195-209",
note = "cited By (since 1996)6",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0035311342&partnerID=40&md5=394b74ac81a1a6fabd22fe81895cf98e",
affiliation = "Robotics Group, Department of Mechanical and Aeronautical Engineering, University of Patras, 26500 Patra, Greece",
abstract = "In this paper, a representational model is proposed for the description and transformation of three-dimensional geometric entities in computer graphics. The structure of the proposed representation is based on dual unit vectors, while the corresponding transformations are carried out through dual unit quaternions or dual orthogonal matrices. The main advantage of this representation is its compactness since the additional useful geometric characteristics of a represented curve or surface such as a tangent or normal vector are incorporated within the actual representational structure itself. Rotations, translations and view transformations are naturally expressed using the concept of screw displacement, while scaling is accomplished utilizing the moment vector of each dual line. Furthermore, an analysis of the transform operator based on dual unit quaternions is presented in order to ascertain an efficient formula to be used in the implementation of a computational algorithm for computer animation. Finally, an analytical comparison between the proposed representational model and the usual homogeneous model in computer animation is presented showing the merits of our method."
}

P N Azariadis and N A Aspragathos. On using planar developments to perform texture mapping on arbitrarily curved surfaces. Computers and Graphics (Pergamon) 24(4):539-554, 2000. URL, AbstractThis paper introduces a method for applying texture from a two-dimensional domain to a three-dimensional surface which is divided into two stages: the pre-processing stage, where a proper planar development of the three-dimensional surface is generated and the stage of mapping texture from the plane to the given surface. Several techniques for generating planar developments are studied and a new technique for surface flattening is proposed. Using this technique it is possible to control the local mapping accuracy. A new mapping method and a set of indices for evaluating the mapping accuracy are proposed. The accuracy indices are derived through the numerical method of singular-value decomposition. To reduce aliasing a space-variant filter, which can be incorporated within the two stages of the introduced texture mapping technique is developed. Finally, various applications are worked out to illustrate the effectiveness of the techniques proposed in this paper.BibTeX

@article{Azariadis2000539,
author = "Azariadis, P.N. and Aspragathos, N.A.",
title = "On using planar developments to perform texture mapping on arbitrarily curved surfaces",
journal = "Computers and Graphics (Pergamon)",
year = 2000,
volume = 24,
number = 4,
pages = "539-554",
note = "cited By (since 1996)12",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0034248512&partnerID=40&md5=046907c03abe1c2f294ba46b87a2a682",
affiliation = "Laboratory of Machine Design, Department of Mechanical and Aeronautical Engineering, University of Patras, 26500 Patras, Greece",
abstract = "This paper introduces a method for applying texture from a two-dimensional domain to a three-dimensional surface which is divided into two stages: the pre-processing stage, where a proper planar development of the three-dimensional surface is generated and the stage of mapping texture from the plane to the given surface. Several techniques for generating planar developments are studied and a new technique for surface flattening is proposed. Using this technique it is possible to control the local mapping accuracy. A new mapping method and a set of indices for evaluating the mapping accuracy are proposed. The accuracy indices are derived through the numerical method of singular-value decomposition. To reduce aliasing a space-variant filter, which can be incorporated within the two stages of the introduced texture mapping technique is developed. Finally, various applications are worked out to illustrate the effectiveness of the techniques proposed in this paper."
}

C J Tsaprounis and N A Aspragathos. Adaptive tracking controller for rigid-link elastic-joint robots with link acceleration estimation. Journal of Intelligent and Robotic Systems: Theory and Applications 27(1-2):67-83, 2000. URL, AbstractThis paper presents a adaptive switching control scheme for elastic joint robot manipulators. The characteristics of both flexible and rigid subsystems are assumed unknown except the joint stiffness. An adaptive estimator compensates the uncertainty due to the unknown robot characteristics. The actuators and links position, velocity and an estimation of the link acceleration are used as feedback to the control law. A filter is designed to estimate the links acceleration and its accuracy is insured by the linear control theory. Lyapunov theory is used to verify the asymptotic stability of the control law. The performance of the proposed control method is tested using a simulated planar robot with two rotational degrees of freedom for high and low joint stiffness.BibTeX

@article{Tsaprounis200067,
author = "Tsaprounis, C.J. and Aspragathos, N.A.",
title = "Adaptive tracking controller for rigid-link elastic-joint robots with link acceleration estimation",
journal = "Journal of Intelligent and Robotic Systems: Theory and Applications",
year = 2000,
volume = 27,
number = "1-2",
pages = "67-83",
note = "cited By (since 1996)4",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0033640324&partnerID=40&md5=bd91df7f9b9b02d3487db34c5bb420c6",
affiliation = "Dept. of Mech. and Aero. Engineering, University of Patras, Patras 26500, Greece",
abstract = "This paper presents a adaptive switching control scheme for elastic joint robot manipulators. The characteristics of both flexible and rigid subsystems are assumed unknown except the joint stiffness. An adaptive estimator compensates the uncertainty due to the unknown robot characteristics. The actuators and links position, velocity and an estimation of the link acceleration are used as feedback to the control law. A filter is designed to estimate the links acceleration and its accuracy is insured by the linear control theory. Lyapunov theory is used to verify the asymptotic stability of the control law. The performance of the proposed control method is tested using a simulated planar robot with two rotational degrees of freedom for high and low joint stiffness."
}

C J Tsaprounis and N A Aspragathos. Sliding mode with adaptive estimation force control of robot manipulators interacting with an unknown passive environment. Robotica 17(4):447-458, 1999. URL, AbstractIn this paper, a force control algorithm for robot manipulators is introduced, where the dynamics of non-rigid environment interacting with the robot is assumed unknown. The controller design is based on the combination of sliding mode control techniques and the adaptive estimation theory, so the introduced controller compensates the structured or unstructured uncertainty of the environment. The main source of feedback information is received from a wrist force sensor. The designed controller includes additional absorption terms in order to minimise end-point velocity error and to suppress the impact effects at the beginning of the force application.BibTeX

@article{Tsaprounis1999447,
author = "Tsaprounis, C.J. and Aspragathos, N.A.",
title = "Sliding mode with adaptive estimation force control of robot manipulators interacting with an unknown passive environment",
journal = "Robotica",
year = 1999,
volume = 17,
number = 4,
pages = "447-458",
note = "cited By (since 1996)6",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0032644165&partnerID=40&md5=eb404c13eda3a5797920d3fe5c1d3c1d",
affiliation = "University of Patras, Dept. of Mech. and Aero. Engineering, Patras 26500, Greece",
abstract = "In this paper, a force control algorithm for robot manipulators is introduced, where the dynamics of non-rigid environment interacting with the robot is assumed unknown. The controller design is based on the combination of sliding mode control techniques and the adaptive estimation theory, so the introduced controller compensates the structured or unstructured uncertainty of the environment. The main source of feedback information is received from a wrist force sensor. The designed controller includes additional absorption terms in order to minimise end-point velocity error and to suppress the impact effects at the beginning of the force application."
}

A C Nearchou, N A Aspragathos and D P Sofotassios. Reducing the complexity of robot's scene for faster collision detection. Journal of Intelligent and Robotic Systems: Theory and Applications 26(1):79-89, 1999. URL, AbstractIn many real-life industrial applications such as welding and painting, the hand tip of a robot manipulator must follow a desired Cartesian curve while its body avoids collisions with obstacles in its environment. Collision detection is an absolutely essential task for any robotic manipulators in order to operate safely and effectively in cluttered environments. A significant factor that influences the complexity of the collision detection problem is the obstacles' density, i.e., the total number of obstacles in the robot's environment. In this paper, a heuristic algorithm for approximating the collision detection problem into a simpler one is presented. The algorithm reduces the number of obstacles that must be examined during the robot's motion by applying efficient techniques from computational geometry. The algorithm runs in time O(max(n2 log m, nm)), and uses O(n2+mn) space; with n being the number of obstacles in the robot's workspace, and m the total number of obstacles' vertices. Both costs are worst-case bounds.BibTeX

@article{Nearchou199979,
author = "Nearchou, A.C. and Aspragathos, N.A. and Sofotassios, D.P.",
title = "Reducing the complexity of robot's scene for faster collision detection",
journal = "Journal of Intelligent and Robotic Systems: Theory and Applications",
year = 1999,
volume = 26,
number = 1,
pages = "79-89",
note = "cited By (since 1996)3",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0032595779&partnerID=40&md5=cf9f3b61e9c0c4b03d692577577e86e1",
affiliation = "Dept. of Mech. Eng. and Aeronautics, University of Patras, 26 500 Patras, Greece; Dept. of Comp. Eng. and Informatics, University of Patras, 26 500 Patras, Greece; Computer Technology Institute, 3 Kolokotroni Str., 26 221 Patras, Greece",
abstract = "In many real-life industrial applications such as welding and painting, the hand tip of a robot manipulator must follow a desired Cartesian curve while its body avoids collisions with obstacles in its environment. Collision detection is an absolutely essential task for any robotic manipulators in order to operate safely and effectively in cluttered environments. A significant factor that influences the complexity of the collision detection problem is the obstacles' density, i.e., the total number of obstacles in the robot's environment. In this paper, a heuristic algorithm for approximating the collision detection problem into a simpler one is presented. The algorithm reduces the number of obstacles that must be examined during the robot's motion by applying efficient techniques from computational geometry. The algorithm runs in time O(max(n2 log m, nm)), and uses O(n2+mn) space; with n being the number of obstacles in the robot's workspace, and m the total number of obstacles' vertices. Both costs are worst-case bounds."
}

V C Moulianitis, A J Dentsoras and N A Aspragathos. Knowledge-based system for the conceptual design of grippers for handling fabrics. Artificial Intelligence for Engineering Design, Analysis and Manufacturing: AIEDAM 13(1):13-25, 1999. URL, AbstractThe paper presents a knowledge-based system (KBS) for the conceptual design of grippers for handling fabrics. Its main purpose is the integration of the domain knowledge in a single system for the systematic design of this type of grippers. The knowledge presented, in terms of gripper, material and handling process, are classified. The reasoning strategy is based upon a combination of a depth-first search method and a heuristic method. The heuristic search method finds a final solution from a given set of feasible solutions and can synthesize new solutions to accomplish the required specifications. Details of the main features of the system are given, including its ability to take critical design decisions according to four criteria, weighted by the designer. The knowledge-based system was implemented in the Kappa P.C. 2.3.2 environment. Two examples are given to illustrate some critical aspects concerning the KBS development, to explain the operation of the proposed searching heuristic method, and to show its effectiveness in producing design concepts for grippers.BibTeX

@article{Moulianitis199913,
author = "Moulianitis, V.C. and Dentsoras, A.J. and Aspragathos, N.A.",
title = "Knowledge-based system for the conceptual design of grippers for handling fabrics",
journal = "Artificial Intelligence for Engineering Design, Analysis and Manufacturing: AIEDAM",
year = 1999,
volume = 13,
number = 1,
pages = "13-25",
note = "cited By (since 1996)14",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0032639304&partnerID=40&md5=55629aaf3f84d108546d316b1e604946",
affiliation = "University of Patras, Mech. Eng. and Aero. Department, 26500 Patras, Greece",
abstract = "The paper presents a knowledge-based system (KBS) for the conceptual design of grippers for handling fabrics. Its main purpose is the integration of the domain knowledge in a single system for the systematic design of this type of grippers. The knowledge presented, in terms of gripper, material and handling process, are classified. The reasoning strategy is based upon a combination of a depth-first search method and a heuristic method. The heuristic search method finds a final solution from a given set of feasible solutions and can synthesize new solutions to accomplish the required specifications. Details of the main features of the system are given, including its ability to take critical design decisions according to four criteria, weighted by the designer. The knowledge-based system was implemented in the Kappa P.C. 2.3.2 environment. Two examples are given to illustrate some critical aspects concerning the KBS development, to explain the operation of the proposed searching heuristic method, and to show its effectiveness in producing design concepts for grippers."
}

N A Aspragathos and J K Dimitros. A comparative study of three methods for robot kinematics. IEEE Transactions on Systems, Man, and Cybernetics, Part B: Cybernetics 28(2):135-145, 1998. URL, AbstractThree methods for the formulation of the kinematic equations of robots with rigid links are presented in this paper. The first and most common method in the robotics community is based on 4 x 4 homogeneous matrix transformation, the second one is based on Lie algebra, and the third one on screw theory expressed via dual quaternions algebra. These three methods are compared in this paper for their use in the kinematic analysis of robot arms. The basic theory and the transformation operators, upon which every method is based, are referenced. Three analytic algorithms are presented for the solution of the direct kinematic problem corresponding to each method, and the geometric significance of the transformation operators and parameters is explained. Finally, a comparative study on the computation and storage requirements for the three methods is worked out.BibTeX

@article{Aspragathos1998135,
author = "Aspragathos, N.A. and Dimitros, J.K.",
title = "A comparative study of three methods for robot kinematics",
journal = "IEEE Transactions on Systems, Man, and Cybernetics, Part B: Cybernetics",
year = 1998,
volume = 28,
number = 2,
pages = "135-145",
note = "cited By (since 1996)36",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0001802987&partnerID=40&md5=6fd1e38a89ef8737925db0ae5f009f62",
affiliation = "Mechanical and Aeronautics Engineering Department, University of Patras, Patras 26500, Greece",
abstract = "Three methods for the formulation of the kinematic equations of robots with rigid links are presented in this paper. The first and most common method in the robotics community is based on 4 x 4 homogeneous matrix transformation, the second one is based on Lie algebra, and the third one on screw theory expressed via dual quaternions algebra. These three methods are compared in this paper for their use in the kinematic analysis of robot arms. The basic theory and the transformation operators, upon which every method is based, are referenced. Three analytic algorithms are presented for the solution of the direct kinematic problem corresponding to each method, and the geometric significance of the transformation operators and parameters is explained. Finally, a comparative study on the computation and storage requirements for the three methods is worked out."
}

C J Tsaprounis and N Aspragathos. Contact point identification in robot assembly strategies under uncertainty. Robotica 16(6):679-690, 1998. URL, AbstractIn this paper a method for the reduction of the uncertainties in robotised assembly process is presented. The generated assembly strategies are based on the determination of the contact points. The assembly task is divided in two main subtasks, the initial and the main. To reduce the uncertainty of the process a deliberate misalignment of the peg is used. This paper is focused on the determination of the position and the forces at the contact points between the peg and hole under uncertainty. The available data are the force signal retrieved from the force sensor, the geometry of the assembly parts and the geometry of the robot. The analysis presented in this paper is a part of a knowledge-based system, which generates assembly strategies under the presence of uncertainties.BibTeX

@article{Tsaprounis1998679,
author = "Tsaprounis, C.J. and Aspragathos, N.",
title = "Contact point identification in robot assembly strategies under uncertainty",
journal = "Robotica",
year = 1998,
volume = 16,
number = 6,
pages = "679-690",
note = "cited By (since 1996)8",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0032205819&partnerID=40&md5=72725cc3151941343d766d97f761b5ce",
affiliation = "University of Patras, Dept. of Mech. and Aero. Engineering, Patras 26500, Greece",
abstract = "In this paper a method for the reduction of the uncertainties in robotised assembly process is presented. The generated assembly strategies are based on the determination of the contact points. The assembly task is divided in two main subtasks, the initial and the main. To reduce the uncertainty of the process a deliberate misalignment of the peg is used. This paper is focused on the determination of the position and the forces at the contact points between the peg and hole under uncertainty. The available data are the force signal retrieved from the force sensor, the geometry of the assembly parts and the geometry of the robot. The analysis presented in this paper is a part of a knowledge-based system, which generates assembly strategies under the presence of uncertainties."
}

A C Nearchou and N A Aspragathos. Collision-Free Cartesian Trajectory Generation Using Raster Scanning and Genetic Algorithms. Journal of Intelligent and Robotic Systems: Theory and Applications 23(2-4):351-377, 1998. URL, AbstractAn algorithm for Cartesian trajectory generation by redundant robots in environments with obstacles is presented. The algorithm combines a raster scanning technique, genetic algorithms and functions for interpolation in the joint coordinates space in order to approximate a desired Cartesian curve by the robot's hand tip under maximum allowed position deviation. A raster scanning technique determines a minimal set of knot points on the desired curve in order to generate a Cartesian trajectory with bounded position approximation error. Genetic algorithms are used to determine an acceptable robot configuration under obstacle avoidance constraints corresponding to a knot point. Robot motion between two successive knot points is finally achieved using well known interpolation techniques in the joint coordinates space. The proposed algorithm is analyzed and its performance is demonstrated through simulated experiments carried out on planar redundant robots.BibTeX

@article{Nearchou1998351,
author = "Nearchou, A.C. and Aspragathos, N.A.",
title = "Collision-Free Cartesian Trajectory Generation Using Raster Scanning and Genetic Algorithms",
journal = "Journal of Intelligent and Robotic Systems: Theory and Applications",
year = 1998,
volume = 23,
number = "2-4",
pages = "351-377",
note = "cited By (since 1996)4",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0032180635&partnerID=40&md5=27507010227807fbafbc427f212e3e3f",
affiliation = "University of Patras, Mechanical Engineering Department, 26 500 Patras, Greece",
abstract = "An algorithm for Cartesian trajectory generation by redundant robots in environments with obstacles is presented. The algorithm combines a raster scanning technique, genetic algorithms and functions for interpolation in the joint coordinates space in order to approximate a desired Cartesian curve by the robot's hand tip under maximum allowed position deviation. A raster scanning technique determines a minimal set of knot points on the desired curve in order to generate a Cartesian trajectory with bounded position approximation error. Genetic algorithms are used to determine an acceptable robot configuration under obstacle avoidance constraints corresponding to a knot point. Robot motion between two successive knot points is finally achieved using well known interpolation techniques in the joint coordinates space. The proposed algorithm is analyzed and its performance is demonstrated through simulated experiments carried out on planar redundant robots."
}

A C Nearchou and N A Aspragathos. A genetic path planning algorithm for redundant articulated robots. Robotica 15(2):213-224, 1997. URL, AbstractIn some daily tasks, such as pick and place, the robot is requested to reach with its hand tip a desired target location while it is operating in its environment. Such tasks become more complex in environments cluttered with obstacles, since the constraint for collision-free movement must be also taken into account. This paper presents a new technique based on genetic algorithms (GAs) to solve the path planning problem of articulated redundant robot manipulators. The efficiency of the proposed GA is demonstrated through multiple experiments carried out on several robots with redundant degrees-of-freedom. Finally, the computational complexity of the proposed solution is estimated, in the worst case.BibTeX

@article{Nearchou1997213,
author = "Nearchou, A.C. and Aspragathos, N.A.",
title = "A genetic path planning algorithm for redundant articulated robots",
journal = "Robotica",
year = 1997,
volume = 15,
number = 2,
pages = "213-224",
note = "cited By (since 1996)13",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0031099156&partnerID=40&md5=a317245fd3995c8f6e3977a964134dad",
affiliation = "Department of Mechanical Engineering, University of Patras, 26 100 Patras, Greece",
abstract = "In some daily tasks, such as pick and place, the robot is requested to reach with its hand tip a desired target location while it is operating in its environment. Such tasks become more complex in environments cluttered with obstacles, since the constraint for collision-free movement must be also taken into account. This paper presents a new technique based on genetic algorithms (GAs) to solve the path planning problem of articulated redundant robot manipulators. The efficiency of the proposed GA is demonstrated through multiple experiments carried out on several robots with redundant degrees-of-freedom. Finally, the computational complexity of the proposed solution is estimated, in the worst case."
}

P Azariadis and N Aspragathos. Design of plane developments of doubly curved surfaces. CAD Computer Aided Design 29(10):675-685, 1997. URL, AbstractThis paper deals with the approximate design of planar developments of doubly curved surfaces and their refinements in order to derive a final plane pattern with limited gaps and overlaps. The hole problem is divided in three stages; the stage of defining the staring guide-strip, the stage of designing the initial pattern and the stage of its refinement. The introduced method dealing with the first stage of the problem is based on elements of the geodesic and Gaussian curvature. In addition, an alternative technique for generating an initial planar development of a doubly curved surface is presented. Two methods for the refinement of the initial pattern are proposed, supported by a set of indices for measuring the accuracy of the flattened component. The first one is based on the surface geometry and the second one on the concept of generalized inverses. By way of illustration, all the proposed methods are presented in parallel with the generation and the refinement of plane patterns of a torus quadrant. In addition, an application of these methods in the 3D surface of a shoe last is demonstrated.BibTeX

@article{Azariadis1997675,
author = "Azariadis, P. and Aspragathos, N.",
title = "Design of plane developments of doubly curved surfaces",
journal = "CAD Computer Aided Design",
year = 1997,
volume = 29,
number = 10,
pages = "675-685",
note = "cited By (since 1996)47",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0031246012&partnerID=40&md5=54eac0d9c99bff40eab5a442fed5164f",
affiliation = "Dept. of Mech. and Aero. Engineering, Laboratory of Machine Design, University of Patras, 26110 Patras, Greece",
abstract = "This paper deals with the approximate design of planar developments of doubly curved surfaces and their refinements in order to derive a final plane pattern with limited gaps and overlaps. The hole problem is divided in three stages; the stage of defining the staring guide-strip, the stage of designing the initial pattern and the stage of its refinement. The introduced method dealing with the first stage of the problem is based on elements of the geodesic and Gaussian curvature. In addition, an alternative technique for generating an initial planar development of a doubly curved surface is presented. Two methods for the refinement of the initial pattern are proposed, supported by a set of indices for measuring the accuracy of the flattened component. The first one is based on the surface geometry and the second one on the concept of generalized inverses. By way of illustration, all the proposed methods are presented in parallel with the generation and the refinement of plane patterns of a torus quadrant. In addition, an application of these methods in the 3D surface of a shoe last is demonstrated."
}

E Dermatas, A Nearchou and N Aspragathos. Error-back-propagation solution to the inverse kinematic problem of redundant manipulators. Robotics and Computer-Integrated Manufacturing 12(4):303-310, 1996. URL, AbstractIn this paper, the inverse kinematics problem of the generalized n-degrees-of-freedom robot is solved using the error-back-propagation algorithm. The efficiency of the proposed solution has been measured for redundant manipulators using 5000 randomly chosen Cartesian coordinates within the robot's workspace. Comparison with two other methods, the well-known pseudoinverse method and a technique based on genetic algorithms, shows that the accuracy of the present method is substantially better.BibTeX

@article{Dermatas1996303,
author = "Dermatas, E and Nearchou, A and Aspragathos, N",
title = "Error-back-propagation solution to the inverse kinematic problem of redundant manipulators",
journal = "Robotics and Computer-Integrated Manufacturing",
year = 1996,
volume = 12,
number = 4,
pages = "303-310",
note = "cited By (since 1996)4",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0030386239&partnerID=40&md5=d22b569c1f1aef87305b419b42f6fa93",
affiliation = "Wire Communications Laboratory, Department of Electrical Engineering, University of Patras, Patras, Greece; Department of Mechanical Engineering, University of Patras, Patras, Greece",
abstract = "In this paper, the inverse kinematics problem of the generalized n-degrees-of-freedom robot is solved using the error-back-propagation algorithm. The efficiency of the proposed solution has been measured for redundant manipulators using 5000 randomly chosen Cartesian coordinates within the robot's workspace. Comparison with two other methods, the well-known pseudoinverse method and a technique based on genetic algorithms, shows that the accuracy of the present method is substantially better."
}

A C Nearchou and N A Aspragathos. Application of genetic algorithms to point-to-point motion of redundant manipulators. Mechanism and Machine Theory 31(3):261-270, 1996. URL, AbstractIn this paper, the problem of point-to-point motion of redundant robot manipulators working in environments with obstacles is considered. The problem is formulated as a constrained optimization problem and is solved using a method based on genetic algorithms (GAs). The objective of this method is to minimize the end-effector's positional error subject to the obstacle avoidance constraints. The efficiency of the proposed method is demonstrated through multiple experiments carried out on a redundant planar manipulator.BibTeX

@article{Nearchou1996261,
author = "Nearchou, A.C. and Aspragathos, N.A.",
title = "Application of genetic algorithms to point-to-point motion of redundant manipulators",
journal = "Mechanism and Machine Theory",
year = 1996,
volume = 31,
number = 3,
pages = "261-270",
note = "cited By (since 1996)10",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0012974331&partnerID=40&md5=2429656e7fc73f174dd40eb1189e301e",
affiliation = "Department of Mechanical Engineering, University of Patras, 26 110 Patras, Greece",
abstract = "In this paper, the problem of point-to-point motion of redundant robot manipulators working in environments with obstacles is considered. The problem is formulated as a constrained optimization problem and is solved using a method based on genetic algorithms (GAs). The objective of this method is to minimize the end-effector's positional error subject to the obstacle avoidance constraints. The efficiency of the proposed method is demonstrated through multiple experiments carried out on a redundant planar manipulator."
}

A C Nearchou and N A Aspragathos. Collision-Free Continuous Path Control of Manipulators using Genetic Algorithms. Journal of Systems Enginering 6:20-32, 1996. BibTeX

A J Dentsoras and N A Aspragathos. Modelling the dynamic characteristics of a robot arm joint. Robotics and Computer Integrated Manufacturing 8(3):157-161, 1991. URL, AbstractThe dynamic behavior of a robot arm has been modelled, taking into account the elasticity and damping of the joints and the backlash introduced by the gear pairs of the transmission mechanism. The links of the robot arm are considered to be rigid and its joints rotational. A technique for automatic formulation of the differential equations of the lumped mass dynamic model of the gear train, incorporating the backlash nonlinearity, has been developed. Each link and the accompanying joint comprise a module. The dynamic equations of the manipulator are formulated through an iterative technique. The algorithm will provide automatic formulation of the dynamic equations of the model of the arm including the referenced nonlinearities of the joint drives. Finally, an application of the algorithm to a planar manipulator arm with two links and two rotational joints is presented.BibTeX

@article{Dentsoras1991157,
author = "Dentsoras, A.J. and Aspragathos, N.A.",
title = "Modelling the dynamic characteristics of a robot arm joint",
journal = "Robotics and Computer Integrated Manufacturing",
year = 1991,
volume = 8,
number = 3,
pages = "157-161",
note = "cited By (since 1996)0",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-44949286131&partnerID=40&md5=b3bba3d4b2778511d62506c4d4363ffb",
affiliation = "Mechanical Engineering Department, University of Patras, 26000 Patras, Greece",
abstract = "The dynamic behavior of a robot arm has been modelled, taking into account the elasticity and damping of the joints and the backlash introduced by the gear pairs of the transmission mechanism. The links of the robot arm are considered to be rigid and its joints rotational. A technique for automatic formulation of the differential equations of the lumped mass dynamic model of the gear train, incorporating the backlash nonlinearity, has been developed. Each link and the accompanying joint comprise a module. The dynamic equations of the manipulator are formulated through an iterative technique. The algorithm will provide automatic formulation of the dynamic equations of the model of the arm including the referenced nonlinearities of the joint drives. Finally, an application of the algorithm to a planar manipulator arm with two links and two rotational joints is presented."
}

N A Aspragathos. Assembly strategies for parts with a plane of symmetry. Robotica 9(pt 2):189-195, 1991. URL, AbstractThis paper describes the development of assembly strategies based on hybrid force/position control. The assembly strategies developed are confined to the large class of assembly tasks defined as a peg-in-the-hole assembly having a plane of symmetry passing through the axis of insertion. The basic idea to develop a robotic system for programmable assembly is presented. This system can currently operate controlled manipulators with minor modifications, i.e. if a force/torque sensor and proper software for hybrid control are provided. The principles of writing assembly strategies are analysed and examples of more complex assembly tasks than the classic round peg-in-the-hole are discussed in detail.BibTeX

@article{Aspragathos1991189,
author = "Aspragathos, N.A.",
title = "Assembly strategies for parts with a plane of symmetry",
journal = "Robotica",
year = 1991,
volume = 9,
number = "pt 2",
pages = "189-195",
note = "cited By (since 1996)5",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0026142777&partnerID=40&md5=d6e4bb6e37bae3ad55bc2f5b886fa13e",
affiliation = "Univ of Patras, Patras, Greece",
abstract = "This paper describes the development of assembly strategies based on hybrid force/position control. The assembly strategies developed are confined to the large class of assembly tasks defined as a peg-in-the-hole assembly having a plane of symmetry passing through the axis of insertion. The basic idea to develop a robotic system for programmable assembly is presented. This system can currently operate controlled manipulators with minor modifications, i.e. if a force/torque sensor and proper software for hybrid control are provided. The principles of writing assembly strategies are analysed and examples of more complex assembly tasks than the classic round peg-in-the-hole are discussed in detail."
}

P F Rizos, N Aspragathos and A D Dimarogonas. Identification of crack location and magnitude in a cantilever beam from the vibration modes. Journal of Sound and Vibration 138(3):381-388, 1990. URL, AbstractMeasurement of flexural vibrations of a cantilever beam with rectangular cross-section having a transverse surface crack extending uniformly along the width of the beam and analytical results are used to relate the measured vibration modes to the crack location and depth. From the measured amplitudes at two points of the structure vibrating at one of its natural modes, the respective vibration frequency and an analytical solution of the dynamic response, the crack location can be found and depth can be estimated with satisfactory accuracy. The method can be used to identify cracks in structures by measuring its modal characteristics. It is a non-destructive testing method for crack identification, and it is applicable to structures for which a structural analysis is available. The main features of the method are as follows: (a) it requires amplitude measurements at two positions of the structure only; (b) it is applicable to all one-dimensional structures; (c) it demands modest computational effort; (d) it is an accurate, simple and easy to handle method having the advantage that the measurements may be carried out in situ with rather simple equipment.BibTeX

@article{Rizos1990381,
author = "Rizos, P.F and Aspragathos, N and Dimarogonas, A.D",
title = "Identification of crack location and magnitude in a cantilever beam from the vibration modes",
journal = "Journal of Sound and Vibration",
year = 1990,
volume = 138,
number = 3,
pages = "381-388",
note = "cited By (since 1996)357",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0025703027&partnerID=40&md5=4567528c80d975e5a116efb97c43ebb6",
affiliation = "Mechanical Engineering Department, University of Patras, Patras, Greece; Department of Mechanical Engineering, Washington University, St. Louis, MO 63130, United States",
abstract = "Measurement of flexural vibrations of a cantilever beam with rectangular cross-section having a transverse surface crack extending uniformly along the width of the beam and analytical results are used to relate the measured vibration modes to the crack location and depth. From the measured amplitudes at two points of the structure vibrating at one of its natural modes, the respective vibration frequency and an analytical solution of the dynamic response, the crack location can be found and depth can be estimated with satisfactory accuracy. The method can be used to identify cracks in structures by measuring its modal characteristics. It is a non-destructive testing method for crack identification, and it is applicable to structures for which a structural analysis is available. The main features of the method are as follows: (a) it requires amplitude measurements at two positions of the structure only; (b) it is applicable to all one-dimensional structures; (c) it demands modest computational effort; (d) it is an accurate, simple and easy to handle method having the advantage that the measurements may be carried out in situ with rather simple equipment."
}

N A Aspragathos, Hopkins S.H., Morgan C. and Bland C.. The Development of a Micromanipulator using Continuous Feedback Control for Automatic Assembly. System Science 15(4), 1989. BibTeX

@article{Aspraga4151989,
author = "Aspragathos, N. A. and Hopkins S.H. and Morgan C. and Bland C.",
title = "The Development of a Micromanipulator using Continuous Feedback Control for Automatic Assembly",
journal = "System Science",
year = 1989,
volume = 15,
number = 4
}

T Lianos, D Kiritsis and N Aspragathos. A direct algorithm for continuous path control of manipulators. Robotics and Computer Integrated Manufacturing 8(2):97-101, 1991. URL, AbstractThis paper presents an algorithm for positioning and orientation of the hand for a redundant or non-redundant manipulator along a continuous path in space. This algorithm minimizes the distance between the actual position of the tip of the end-effector and the desired path. The algorithm does not use the Jacobian matrix for the inverse kinematics of the robot. It takes full advantage of the resolution of the joint drives, avoids singularity problems, and can be used for both redundant manipulators. The algorithm can be used in any situation where continuus motion of the end-effector is required in an open loop mode.BibTeX

@article{Lianos199197,
author = "Lianos, T. and Kiritsis, D. and Aspragathos, N.",
title = "A direct algorithm for continuous path control of manipulators",
journal = "Robotics and Computer Integrated Manufacturing",
year = 1991,
volume = 8,
number = 2,
pages = "97-101",
note = "cited By (since 1996)1",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-2342544080&partnerID=40&md5=779d68b27e0af169cf62a60defe4f811",
affiliation = "Department of Mechanical Engineering, University of Patras, Patras, Greece",
abstract = "This paper presents an algorithm for positioning and orientation of the hand for a redundant or non-redundant manipulator along a continuous path in space. This algorithm minimizes the distance between the actual position of the tip of the end-effector and the desired path. The algorithm does not use the Jacobian matrix for the inverse kinematics of the robot. It takes full advantage of the resolution of the joint drives, avoids singularity problems, and can be used for both redundant manipulators. The algorithm can be used in any situation where continuus motion of the end-effector is required in an open loop mode."
}

N A Aspragathos. Program for torsional dynamic modelling of drive systems and fatigue life prediction. Computer-Aided Design 20(9):555-563, 1988. URL, AbstractThe paper describes the work that has been carried out to develop a program for torsional dynamic lumped simulation of drive systems. This modelling is based on the modular concept and includes nonlinearities of the system and system disturbances. The equations of the model are formed automatically. In addition, a procedure for automatic computation of fatigue life expenditure due to dynamic loading of the shafts and gear teeth is incorporated. The aim of the development of such a program is to provide a useful tool for designers of such systems. With this program, the designer can test the dynamic behaviour of a drive system and estimate the fatigue life expenditure of the dynamically loaded components.BibTeX

@article{Aspragathos1988555,
author = "Aspragathos, N.A.",
title = "Program for torsional dynamic modelling of drive systems and fatigue life prediction",
journal = "Computer-Aided Design",
year = 1988,
volume = 20,
number = 9,
pages = "555-563",
note = "cited By (since 1996)0",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0024110908&partnerID=40&md5=13e0e271259b5774feb7c6f1fa700224",
affiliation = "Mechanical Engineering Department, University of Patras, Patras, Greece",
abstract = "The paper describes the work that has been carried out to develop a program for torsional dynamic lumped simulation of drive systems. This modelling is based on the modular concept and includes nonlinearities of the system and system disturbances. The equations of the model are formed automatically. In addition, a procedure for automatic computation of fatigue life expenditure due to dynamic loading of the shafts and gear teeth is incorporated. The aim of the development of such a program is to provide a useful tool for designers of such systems. With this program, the designer can test the dynamic behaviour of a drive system and estimate the fatigue life expenditure of the dynamically loaded components."
}

D Michalopoulos, N Aspragathos and A D Dimarogonas. Fatigue damage of gear teeth in speed reducers moving heavy rotors.. TRANS. ASME J. VIB. ACOUST. STRESS & RELIAB. DES. 109(2 , Apr. 1987):196-200, 1987. URL, AbstractAn analytical investigation was undertaken of the dynamic loading and fatigue of the gear teeth of turbine generator turning gear mechanisms during engagement, using a nonlinear function of speed and load for the coefficient of friction, which was determined experimentally under stick slip conditions and considering backlash. When heavy rotors are rotating on fluid bearings at low speeds, they are sometimes subject to stick slip. The fatigue damage resulting in such systems due to the stick slip self excited vibrations developed on the bearings, and the backlash of the gear teeth can be predicted by a simulation procedure described in this paper. The effects of some design parameters on the fatigue life reduction and tooth loading are also investigated so that they may be used in design.BibTeX

@article{Michalopoulos196,
author = "Michalopoulos, D. and Aspragathos, N. and Dimarogonas, A.D.",
title = "Fatigue damage of gear teeth in speed reducers moving heavy rotors.",
journal = "TRANS. ASME J. VIB. ACOUST. STRESS & RELIAB. DES.",
volume = 109,
year = 1987,
number = "2 , Apr. 1987",
pages = "196-200",
note = "cited By (since 1996)0",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0013767167&partnerID=40&md5=226718490556e4714bbfea4f5fd90a97",
abstract = "An analytical investigation was undertaken of the dynamic loading and fatigue of the gear teeth of turbine generator turning gear mechanisms during engagement, using a nonlinear function of speed and load for the coefficient of friction, which was determined experimentally under stick slip conditions and considering backlash. When heavy rotors are rotating on fluid bearings at low speeds, they are sometimes subject to stick slip. The fatigue damage resulting in such systems due to the stick slip self excited vibrations developed on the bearings, and the backlash of the gear teeth can be predicted by a simulation procedure described in this paper. The effects of some design parameters on the fatigue life reduction and tooth loading are also investigated so that they may be used in design."
}

N Aspragathos and A Dimarogonas. The Effects of Some System Parameters on the Fatigue Life Reduction of Turbine Generator Shafts due to Electrical Transients. IEEE transactions on power apparatus and systems PAS-103(8):2308-2316, 1984. URL, AbstractThe effect of some important system parameters on the fatigue life reduction of turbogenerator rotor shafts, due to large scale disturbances of the HV electrical network, is investigated. These system design parameters are relevant with the turbine, the generator and the network. Moreover, the effect of the out-of-phase synchronization angle on the fatigue life reduction of the rotor shaft is investigated. These studies were carried out using system simulation techniques while the hysteretic damping was expressed by a novel non-linear expression.BibTeX

@article{Aspragathos19842308,
author = "Aspragathos, N. and Dimarogonas, A.",
title = "The Effects of Some System Parameters on the Fatigue Life Reduction of Turbine Generator Shafts due to Electrical Transients",
journal = "IEEE transactions on power apparatus and systems",
year = 1984,
volume = "PAS-103",
number = 8,
pages = "2308-2316",
note = "cited By (since 1996)2",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0021479886&partnerID=40&md5=6715935e1f96d0d50ffeade39d6c3db3",
abstract = "The effect of some important system parameters on the fatigue life reduction of turbogenerator rotor shafts, due to large scale disturbances of the HV electrical network, is investigated. These system design parameters are relevant with the turbine, the generator and the network. Moreover, the effect of the out-of-phase synchronization angle on the fatigue life reduction of the rotor shaft is investigated. These studies were carried out using system simulation techniques while the hysteretic damping was expressed by a novel non-linear expression."
}

S Panteliou, N Aspragathos and A Dimarogonas. Thermal effects on rotating shafts due to electrical transients causing plastic deformation. Ingenieur-Archiv 53(3):173-179, 1983. URL, AbstractDuring transient torsional vibration of rotating shafts, heat is generated which may affect its operational integrity. The shaft modelled as a cylinder of infinite length heated by way of a transient torsional vibration of variable amplitude is investigated and an expression for the maximum surface temperature is obtained. Diagrams with the appropriate dimensionless parameters are presented together with a numerical example corresponding to an existing turbine-generator system. Both plastic deformation and material damping is considered. It is shown that substantial temperatures can be developed as a result of this mechanism of heat generation. This quantifies the belief that this phenomenon was the reason for a major generator failure in a power system, during an electrical disturbance.BibTeX

@article{Panteliou1983173,
author = "Panteliou, S. and Aspragathos, N. and Dimarogonas, A.",
title = "Thermal effects on rotating shafts due to electrical transients causing plastic deformation",
journal = "Ingenieur-Archiv",
year = 1983,
volume = 53,
number = 3,
pages = "173-179",
note = "cited By (since 1996)0",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0020544236&partnerID=40&md5=f38bb5c0dc51ec78b7c796e531e72bef",
affiliation = "Machine Design Laboratory, University of Patras, Patras, Greece",
abstract = "During transient torsional vibration of rotating shafts, heat is generated which may affect its operational integrity. The shaft modelled as a cylinder of infinite length heated by way of a transient torsional vibration of variable amplitude is investigated and an expression for the maximum surface temperature is obtained. Diagrams with the appropriate dimensionless parameters are presented together with a numerical example corresponding to an existing turbine-generator system. Both plastic deformation and material damping is considered. It is shown that substantial temperatures can be developed as a result of this mechanism of heat generation. This quantifies the belief that this phenomenon was the reason for a major generator failure in a power system, during an electrical disturbance."
}

N Aspragathos and A Dimarogonas. Torsional Fatigue Life Reduction in Turbogenerators due to Large Scale Disturbances under Fast Valving Control. Archiv fur Elektrotechnik Berlin 64(5):275-284, 1982. URL, AbstractThe use of fast valving control may have a significant effect on life reduction due to torsional fatigue of rotor shafts. In this paper an analytical and numerical study has been applied to calculate the fatigue life reduction for large scale transient electrical disturbances under speed governor control of turbogenerator with reheater and under modern fast-valving control in the intercept valve after the reheater. Finally, the fatigue life reduction was compared to the improvement of first swing stability under the two control systems.BibTeX

@article{Aspragathos1982275,
author = "Aspragathos, N. and Dimarogonas, A.",
title = "Torsional Fatigue Life Reduction in Turbogenerators due to Large Scale Disturbances under Fast Valving Control",
journal = "Archiv fur Elektrotechnik Berlin",
year = 1982,
volume = 64,
number = 5,
pages = "275-284",
url = "https://www.scopus.com/inward/record.url?eid=2-s2.0-0019914664&partnerID=40&md5=187ef023e78551bf164803e007f200b8",
abstract = "The use of fast valving control may have a significant effect on life reduction due to torsional fatigue of rotor shafts. In this paper an analytical and numerical study has been applied to calculate the fatigue life reduction for large scale transient electrical disturbances under speed governor control of turbogenerator with reheater and under modern fast-valving control in the intercept valve after the reheater. Finally, the fatigue life reduction was compared to the improvement of first swing stability under the two control systems."
}

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